The Montreux Convention: A Model for Hormuz?

Before the 20^th century, customary international law was the principal source of maritime law. Broadly, customary law embraced freedom of the high seas, a narrow territorial sea (as far as a gun could be fired), and the authority of a flag state over its vessels. Latterly much of this was codified in the 1982 UN Convention on the Law of the Sea (UNCLOS),[1] which is now the international treaty covering territorial waters, exclusive economic zones, continental shelves and the high seas. Custom still binds states that have not ratified UNCLOS, notably the United States: the United States signed UNCLOS in 1994, but the US Senate has never ratified the treaty.[2] Washington nonetheless treats most of the Convention’s navigational provisions, including the rights of innocent passage and of transit passage regimes, as the binding law. UNCLOS remains the route by which contested norms, such as artificial islands and deep-sea mining, are evaluated before being settled in treaty law.

So, customary law predates UNCLOS, while both cover the authority of coastal states and the freedom of states to use the seas for navigation, commerce and communication.

But what can history tell us?

The Danish Sound Toll

The Øresund, between Denmark and Sweden, is the principal sea route between the Baltic and the Atlantic world. Trade in timber, grain, tar, hemp, iron and copper underpinned Northern European commerce and naval power, so control of the Sound meant control of a strategic economic artery. The Danish Sound Toll, or Øresundstolden, became one of the most important assertions of maritime power in European history. Established formally in 1429 by King Eric of Pomerania[3] and collected at Helsingør, the toll lasted until 1857. Every vessel, whatever its flag, had to pay before passing. Charges were based on declared cargo value, and Denmark’s right to buy cargo at that value encouraged truthful declarations. At its height, the toll produced about two-thirds of the Danish Crown’s income.[4] The toll repeatedly caused friction and war. Dutch prosperity depended on Baltic commerce, and the Netherlands fought Denmark over rates, while Sweden’s resentment of Danish control of the Sound fuelled Dano-Swedish conflict, and England pressed for exemptions because Baltic naval stores were essential for its fleet. The toll therefore exposed a recurring legal and strategic problem: whether a coastal state could exploit geography to tax international commerce, or whether wider freedom of navigation should prevail.

By the mid-19^th century the toll had become politically indefensible before free-trade ideas, steam-powered shipping, and sustained pressure from maritime powers, not least the United States. So, in 1857 the Copenhagen Treaty guaranteed permanent free navigation through the Øresund for ships of all nations, and abolished the Sound Toll while Denmark received a one-off compensatory payment from the principal maritime powers.[5]

The abolition of the Sound Toll anticipated principles later reflected in UNCLOS: that innocent passage through an international strait cannot be monetised as a sovereign privilege; that straits used for international navigation impose duties beyond ordinary territorial control; and that major trading states have a shared interest in preventing strategic waterways from being privatised. The lesson was practical as well as legal. Ending the Danish Crown’s exploitation of a chokepoint required sustained multilateral pressure, the credible threat of force and financial compensation, not moral argument alone. The modern law of international straits, including UNCLOS transit passage, rests partly on that struggle.

The Law at Sea: Between the Sound Toll and Montreux (1857–1936)

However, the abolition of the Sound Toll left a legal vacuum: the principle that no state should profit from geography at the expense of free commerce was established, but no positive international framework existed to enforce it. The period from 1857 to 1936 was one of the most turbulent and formative in the history of maritime law, marked by rapid technological change, imperial competition, a world war, and the first serious attempts to replace custom and bilateral treaty with multilateral order. Freedom of navigation in international straits remained a matter of customary law which benefited Western sea powers, Britain, France, the Netherlands and the emerging United States, which used diplomatic pressure and the implicit threat of force to keep critical straits open.

The Hague Peace Conference of 1899 produced conventions on the peaceful settlement of disputes and the laws and customs of war on land; the 1907 conference expanded these and added conventions on naval warfare and neutral rights, though neither addressed the general law of the sea.[6] They were however attempts to codify international law. Neither produced a comprehensive law of the sea, but they established lasting principles: the distinction between contraband and innocent cargo, the rights of neutral vessels, the obligation to minimise interference with neutral commerce, and the requirement that blockades be effective to be legally binding. The 1909 Declaration of London on the law of naval war codified these rules but was never ratified by any of the ten signatories, including Britain,[7] and had no binding legal force when the First World War began. The world’s greatest naval powers had the most to gain from freedom of navigation in peacetime and the most to lose from restrictions on their freedom of action in war, and while the 1909 declaration attempted to codify naval warfare law in unprecedented detail, its failure to secure ratification left the underlying tensions at sea unresolved.

It is fair to say that maritime order collapsed during the First World War: customary law was inadequate in the industrial age. Germany’s unrestricted submarine warfare treated all vessels in British waters as legitimate targets regardless of flag or cargo, directly repudiating the Hague principles, while Britain’s counter-blockade was only a little more consistent with the Declaration of London. The Ottoman Empire closed the Dardanelles to Allied shipping from late 1914, severing Russia’s principal warm water supply route, and reopening the Turkish Straits was a central strategic objective of the failed 1915 Gallipoli campaign.[8] The lesson was stark: strait access dependent on the goodwill of a belligerent coastal state was no access at all.

The Turkish Straits

By 1914 the Turkish Straits were already a recurring problem. The 1841 Straits Convention of London closed the Bosphorus and Dardanelles to foreign warships in peacetime; the 1856 Treaty of Paris after the Crimean War neutralised the Black Sea: and the 1878 Treaty of Berlin, following the Russo-Turkish War, closed the Bosphorus and Dardanelles to foreign warships in peacetime under Ottoman supervision.[9] In essence the Straits were renegotiated after conflicts, showing that maritime law in this period was an extension of the balance of power rather than any rules-based order.

The 1923 Treaty of Lausanne, which helped to establish the modern Turkish state, demilitarised the straits and placed supervision of the passage regime under an international straits commission acting within the League of Nations framework, thus stripping Turkey of meaningful sovereignty over its own territorial waters.[10] Atatürk’s government deeply resented this, and it was widely regarded as unsustainable. The 1930 Hague Codification Conference made the first serious attempt in the 20th century to codify the law of the sea regarding territorial waters but ended largely in failure.[11] Delegates could not agree on the breadth of the territorial sea or settle the meaning of innocent passage.

The 1936 Montreux Convention corrected this. A diplomatically resurgent Turkey negotiated the restoration of its sovereignty in exchange for accepting the regulated access which Montreux offered. It was a product of a specific geopolitical moment, rising fascism in Europe, Soviet anxiety about the Black Sea, and British concern about Mediterranean stability, but it drew on 80 years of accumulated practice and failed codification attempts.

The period from 1857 to 1936 is therefore best understood not as a gap in maritime law but as its most intensive learning phase, in which the international community discovered that freedom of navigation in strategic straits could not rest on custom and goodwill alone.

The Montreux Convention is unique in international maritime law: it gives Turkey exceptional control over the Bosphorus and Dardanelles that far exceeds what a later UNCLOS would permit, but as a pre-existing special regime Montreux was preserved.

Regarding civilian vessels in peacetime, free passage is guaranteed for merchant ships of all nations, by day and night, under any flag and with any cargo, without formalities and without any requirement of advance notice: vessels simply communicate their name, flag, tonnage, destination and last port of call to signal stations as they pass. Turkey may levy only the published, non-discriminatory charges set out in the Montreux Convention (sanitary control, lighthouse and buoyage, and life-saving services), calculated to cover the cost of the service rather than to raise revenue; pilotage and towage remain optional rather than compulsory.

Regarding warship transit in peacetime, Turkey possesses exceptional powers. Montreux specifies a notice period before sending a warship through the straits of eight days: “The normal period of notice shall be eight days; but it is desirable that in the case of non-Black Sea Powers this period should be increased to fifteen days.”[12] Among the detailed rules, the aggregate tonnage of all foreign warships in transit at any one time, of whatever origin, is capped at 15,000 tons and their number at nine vessels, with only light surface vessels, minor war vessels and auxiliaries exempted from the cap. Black Sea powers may additionally send larger capital ships through singly, escorted by no more than two destroyers. Aircraft carriers cannot transit the straits at all,[13] submarines of non-Black Sea powers have no right of transit; Black Sea powers may move submarines through only to join or leave their fleet, travelling singly, by day and on the surface.

Turkey’s wartime powers: when Turkey is neutral, belligerent states’ warships are barred from transit; merchant ships of belligerents, and warships of non-belligerent third states, may pass under the peacetime rules. However, when Turkey is a belligerent, the notice, tonnage and other peacetime conditions cease to apply, and passage of warships is left entirely to Turkey’s discretion. Turkey has the same discretion if it considers itself under imminent threat of war. This was last tested in February 2022, when Russia invaded Ukraine. Turkey formally notified the UN Secretary-General and Convention parties on 28 February 2022 that it regarded Russia and Ukraine as belligerents and closed the straits to their warships.[14]

Fees are levied for commercial transit through the Turkish straits, though there is a firm distinction between fees that reimburse for a genuine service and tolls that simply tax the right of passage. The abolition of the Danish Sound Toll confirmed that the latter are impermissible; the former are not only permissible but widely practised.

Under Montreux, Turkey has the sovereign right to set and collect fees for commercial transit through the Bosphorus and Dardanelles, but this power operates within defined constraints. The Convention does not fix fee amounts, but requires that fees be published in advance, be non-discriminatory across flag states, and fall within specific permitted categories.

Lighthouse and navigational aid dues are the clearest lawful charges, recovering the cost of lighthouses, buoys, beacons, radar, etc, provided they are proportionate and non-discriminatory. Buoyage and traffic separation scheme fees may recover the cost of buoyage, monitoring stations and vessel traffic services on the same basis. Pilotage may be strongly recommended and charged where used but should not be made compulsory in a way that turns it into a condition of passage. Sanitary, health and quarantine dues, expressly permitted under Montreux, may cover inspections, quarantine services and fumigation certificates, provided they remain administrative rather than punitive.

Four principles are common to these fees, they: must correspond to a real service provided to the vessel; must not exceed the reasonable cost of that service; must apply equally to all flag states; and must be published in advance and applied predictably. Otherwise the fees may be challenged whether as a breach of Montreux’s notice requirements, or an unlawful toll, or a disguised restriction on navigation, or a breach of UNCLOS and customary law.

Legitimate strait fees must relate to actual operational costs rather than generate sovereign revenue. The Danish Sound Toll produced two-thirds of the Danish Crown’s income precisely because it was a toll on geography, not a service fee; modern international law has – for the time being – firmly closed that door, while coastal states may recover the genuine costs of keeping their straits safe, clean and navigable. Thus Turkey cannot raise fees arbitrarily, and IMO cost-recovery standards provide the benchmark against which the reasonableness of such fees is judged, though Montreux itself creates no formal fee-arbitration mechanism.

United Nations Conference on Law of the Sea

The Third UN Conference on the Law of the Sea (UNCLOS) was convened in 1973 amid growing concern that customary law of the sea no longer matched the political, technological and economic realities of the seas. Nine years of negotiation followed which produced a comprehensive convention, UNCLOS, opened for signature in 1982 and entering into force in 1994.[15]

The principle which interests the author is that under UNCLOS, narrow straits connecting one area of high seas or exclusive economic zone to another, and used for international navigation, are subject to a special regime known as the right of transit passage. Further, these international highways, open to all shipping, may run through the territorial waters of one or more coastal states. This is regarded as a well-established principle of modern international law. All ships and aircraft, including warships and military aircraft, have the right to pass through these straits and no coastal state can suspend this right. The coastal state retains sovereignty over the water but cannot block or impede transit.

The Strait of Hormuz, between Iran and Oman and a critical global oil shipping lane, is but one example of such a strait.[16] Among others are the Strait of Malacca, bordering Malaysia, Indonesia and Singapore and the busiest commercial shipping route in Asia; the Strait of Gibraltar, between Spain and Morocco; and the Strait of Bab-el-Mandeb, connecting the Red Sea to the Gulf of Aden.

Warships also enjoy the right of innocent passage and this right can only be suspended by a coastal state if it is essential for the protection of its security, it must be temporary, confined to specific areas rather than the whole of the territorial sea, non-discriminatory, and formally published with adequate notice. On the other hand, passage becomes non-innocent if a foreign warship conducts weapons exercises, intelligence gathering, launches aircraft, etc. While innocent passage of warships may be suspended temporarily, transit passage can never be suspended, and merchant ships pass as of right. However, innocent passage carries no right of overflight, while transit passage extends overflight rights to aircraft, including military aircraft, provided passage is continuous and expeditious.

The Strait of Hormuz

The Montreux Convention is a product of a specific historical moment: Turkey seeking to reassert sovereignty and great powers willing to trade strategic control for regional stability. It has never been replicated but were the Strait of Hormuz to be governed by a comparable instrument granting Iran and Oman Montreux-style powers, the precedent would be seismic, and other littoral states would almost certainly advance similar claims.

Maybe the present war in the Gulf is another historic opportunity for a convention to govern the Strait of Hormuz. What follows is necessarily speculative.

The territorial seas of Iran and Oman extend across the strait. Iran’s strategic motivation for a change in the rules-based order previously set out in this article is high,[17] Oman’s more moderate. International opposition would be extreme, since the United States, Saudi Arabia and other oil-importing nations would resist any arrangement seen as strengthening Iranian control, the historical precedent is weak, and, unlike Montreux, there is no pre-UNCLOS treaty framework to build on.

Further, Hormuz is a critical chokepoint: roughly a fifth of global petroleum products transit the Strait of Hormuz, alongside a substantial share of global LNG trade routed from Qatari and other Gulf export terminals.[18] Iran controls the northern shore, Oman the southern, and under UNCLOS neither is able to suspend or restrict navigation. Iran has long chafed at this, periodically threatened closure, demanded that foreign warships seek permission to transit its territorial waters, and conducted exercises designed to demonstrate its ability to close the strait. A Montreux-style convention would give Iran the legitimate tools it currently lacks: advance notice requirements, tonnage limits on foreign warships, the ability to exclude certain vessel classes, and the right to close the strait. Oman’s position is more nuanced: with close ties to both the West and Iran, Oman might welcome a formal convention as a framework for de-escalation, provided it were genuinely co-administered rather than Iranian-dominated.

The likelihood of acceptance is therefore very low under current geopolitics, though it might become conceivable in a fundamentally restructured Middle East order.

Towards a New Convention

Any Montreux-style instrument would need to resolve the problems which the 1936 drafters faced and which have grown more complex since: how coastal and user states are distinguished and their interests weighted; how tonnage limits and vessel class restrictions are calibrated in the age of supercarriers, nuclear submarines and drone swarms; what environmental standards apply and who enforces them; how the convention interacts with UN Security Council resolutions on sanctions; and whether it can survive the withdrawal of a major power, as Montreux itself nearly did not survive Soviet pressure in 1946.[19]

However, Montreux endures because it struck a balance every party, however grudgingly, found preferable to the alternatives: Turkey got sovereignty and control, Black Sea states got guaranteed access, non-Black Sea powers got passage rights calibrated to their legitimate interests, and the world got a stable framework that has kept the Turkish Straits from becoming a flashpoint. If Iran shared such powers with Oman over Hormuz, would it be the responsible steward that Turkey has been?

Conclusion: The Case for a Hormuz Convention

Without a formal, binding, multilateral framework, navigation rights depend on the goodwill or military capacity of the coastal states. UNCLOS is probably the most successful international legal instrument ever created, and the Montreux Convention shows that a special regime can work, but when that goodwill fails, as in the present Gulf crisis, UNCLOS offers no adequate remedy.

However, there is no legal, strategic or practical reason why a Montreux-style convention should not govern navigation through Hormuz. Arguments against one are political rather than principled: that Iran cannot be trusted to administer it in good faith, that the United States and its Gulf allies would resist any arrangement legitimising enhanced Iranian authority, and that the precedent might be exploited in other straits. These are the same obstacles that confronted the negotiators of Montreux in 1936, and Montreux was negotiated, nonetheless.

A properly designed Hormuz Convention would not grant Iran unilateral control; the model is Montreux, not the Sound Toll. It would rest on joint administration by Iran and Oman through a permanent joint secretariat with a dispute resolution mechanism, advance notice requirements for warships of non-littoral states with tonnage limits and prohibitions on high-risk vessel classes analogous to Montreux’s restrictions on carriers and submarines, guaranteed transit passage for commercial vessels of all nations with no fees beyond those justified by genuine navigational services, environmental and safety standards enforceable by both littoral states including mandatory AIS operation and MARPOL compliance, a conflict clause modelled on Montreux Articles 19 and 20 under which any closure would require the concurrence of both Iran and Oman and notification to the Security Council, and guaranteed, non-discriminatory access for the vessels of landlocked states dependent on Gulf ports, including the Central Asian republics.

A new Hormuz Convention would place substantive, enforceable responsibilities on Iran and Oman. This would not be a concession to Iran but a constraint on it, in exchange for the legitimate recognition of its role as a coastal state that Montreux already gives Turkey. Iran’s obligations would include guaranteeing commercial transit without interference or threat, a prohibition on using closure as an instrument of political or economic coercion, a duty to maintain navigational aids, search and rescue capacity and anti-pollution response in its sector, and acceptance of international monitoring. In exchange Iran would receive advance notice of warship transits, the ability to exclude certain vessel classes, legitimate fees for navigational services, and, critically, international recognition as co-administrator with Oman of one of the world’s most important waterways. Oman’s responsibilities would be analogous, but its strategic position differs as a consistently neutral state with functioning diplomatic relations to other Gulf states, it is the natural guarantor of a new convention’s integrity and a responsible broker whose participation would give the new convention credibility with external maritime powers and the Gulf states.

The Broader Significance

A Hormuz Convention would do more than govern one strait. It would re-establish a precedent, absent since 1936, that a multilateral special regime for a critical strait can be negotiated even between states in fundamental strategic conflict. It would provide a model for Malacca, Bab-el-Mandeb, etc., and eventually any Arctic routes.

The Danish Sound Toll was ended because the international community decided, after four centuries, that no state should profit from geography at the expense of free commerce. Montreux was negotiated because it decided, after the chaos of the interwar period, that strait governance required a formal multilateral structure. The case for a Hormuz Convention is, at its core, the same case made for Montreux in 1936. The obstacles are real and the political will is currently absent, but the logic is sound, and the cost of inaction, measured in disrupted energy supplies, humanitarian crises and the steady erosion of the rules-based maritime order, will only grow. The question is not whether such a convention is desirable. The question is whether the international community will find the will to negotiate it before the crisis in the Strait of Hormuz makes the answer irrelevant.

Events since this article was first drafted have highlighted the issue. The 2026 Hormuz crisis showed an appetite by both Iran and the United States for monetising strait passage,[20] and the disorder that follows when that appetite is pursued through unilateral threats rather than negotiated multilateral structure. Events also showed signs of contagion when Indonesia briefly raised the same issues,[21] and Houthi militias renewed a copycat blockade at the Bab-el-Mandeb within months.[22]

None of this weakens the case for a Hormuz Convention; if anything, it demonstrates what fills the vacuum when one is absent.

Stop Press: The 2026 Hormuz Crisis

This analysis was overtaken by events within weeks of being written. War broke out between the United States and Iran in 2026,[23] and the fight to reopen the Strait of Hormuz became the live test of every principle set out above. After Iran closed the strait and attacked commercial shipping, the US Navy imposed a blockade on Iranian ports,[24] and on 17 June 2026 the two sides signed the Islamabad Memorandum of Understanding, under which Iran guaranteed free passage for 60 days and agreed to negotiate with Oman on the strait’s future administration and maritime services thereafter.[25] Secretary of State Marco Rubio invoked precisely the toll versus service-fee distinction set out in this article, stating that no country is allowed to charge tolls or fees on an international waterway.[26] President Trump then proposed the opposite: a 20% levy on the cargo value of every vessel transiting the strait, framed as reimbursement for US protection, before reversing course and offering Gulf states investment deals instead.[27] Oman has since presented Iran with a Gulf-backed proposal for a regional mechanism, modelled on the Strait of Malacca’s voluntary-contribution scheme, for joint management of the strait’s navigation, environmental and search-and-rescue services, an arrangement that echoes,[28] without replicating, the joint administration model this article proposes for a Hormuz Convention, and the IMO has restated its institutional opposition to any transit fee.[29] By early August those talks had moved into their final stages: Iran’s foreign ministry said the two sides were close to agreement on an entirely new maritime corridor through the strait, distinct from the existing northern and southern shipping lanes.[30] The war itself remained unresolved, however, with tanker attacks near Oman’s coast resuming in late July and Washington and Tehran trading accusations of bad faith over whether ceasefire talks had even resumed.[31] The Islamabad Memorandum’s 60-day free-passage guarantee is due to lapse around 16 August 2026; Iran has signalled that it will then begin charging, in its own words, “fees for services” rather than tolls, keeping the coming weeks squarely inside the toll-versus-service-fee argument this article makes.[32]

Rather than undermining it, these developments confirm this article’s central argument: absent a negotiated multilateral framework, strait governance defaults to unilateral improvisation, threats and the shadow of force, precisely the pattern which the Montreux Convention successfully ended.

References

[1] United Nations Convention on the Law of the Sea (UNCLOS), opened for signature 10 December 1982, 1833 UNTS 3, entered into force 16 November 1994. International Tribunal for the Law of the Sea, “UNCLOS,” itlos.org.

[2] The United States signed UNCLOS on 29 July 1994; the Senate has never given its advice and consent to ratification. See The Diplomat, “U.S. Ratification of the Law of the Sea Convention” (2017); Congress.gov, S.Res.331, 119th Congress (2025–2026).

[3] The Sound Dues (Øresundstolden) were established in 1429 by King Eric of Pomerania and collected at Helsingør. Wikipedia, “Sound Dues”; Havneguide.dk, “The History of the Sound Tolls.”

[4] At their height the dues supplied roughly two-thirds of the Danish Crown’s income. Wikipedia, “Sound Dues.”

[5] Under the Copenhagen Convention of 1857, Denmark received 33.5 million Danish rigsdaler (roughly 2.1 billion kroner in 2022 terms) from the signatory maritime powers, with Britain and Russia each contributing about a third. Grokipedia, “Copenhagen Convention of 1857”; UK Parliament, Hansard, 5 June 1857.

[6] Hague Peace Conferences of 1899 and 1907. See the Avalon Project, Yale Law School, for the full conventions.

[7] The 1909 Declaration Concerning the Laws of Naval War was signed in London by ten powers, including Britain, but ratified by none; it lapsed after the House of Lords rejected the enabling legislation in 1911. Wikipedia, “London Declaration concerning the Laws of Naval War.”

[8] The Ottoman Empire closed the Dardanelles to Allied shipping from late 1914; the failed 1915 Gallipoli campaign aimed in part to force the Strait open. Encyclopaedia Britannica, “Gallipoli Campaign.”

[9] London Straits Convention, 1841 (barring foreign warships from the straits in peacetime); Treaty of Paris, 1856 (neutralising the Black Sea after the Crimean War); Treaty of Berlin, 1878 (reaffirming the closure principle). Encyclopaedia Britannica, “London Straits Convention”; Oxford Public International Law, “Paris Peace Treaty (1856).”

[10] Treaty of Lausanne, 24 July 1923; the International Straits Commission operated under League of Nations auspices from 1923 until superseded by the Montreux Convention in 1936. Wikipedia, “International Straits Commission.”

[11] League of Nations Codification Conference, The Hague, 1930, failed chiefly over the breadth of the territorial sea. Wikipedia, “League of Nations Codification Conference, 1930”; IILSS, “The Hague Conference for the Codification of International Law (1930).”

[12] Convention Regarding the Regime of the Straits (Montreux Convention), 20 July 1936, Article 13. Full text: Centre for International Law, National University of Singapore.

[13] Montreux Convention, Articles 10–11 and Annex II; because aircraft carriers fall outside the Convention’s “capital ship” exemption, the 15,000-ton/nine-vessel cap on ordinary warship transit effectively excludes them. Digital Commons, University of San Diego Law Review, “Kiev and the Montreux Convention: The Aircraft Carrier That Became a Cruiser”; CIMSEC, “Let Me Get This Strait: The Turkish Straits Question Revisited.”

[14] Turkey formally notified the UN Secretary-General and Montreux parties on 28 February 2022 that it regarded Russia and Ukraine as belligerents under Article 19 and closed the straits to their warships. Naval News, “Turkey Closes the Dardanelles and Bosphorus to Warships” (28 February 2022); Defense News (1 March 2022).

[15] The Third UN Conference on the Law of the Sea was convened in 1973 and concluded in 1982; UNCLOS was opened for signature at Montego Bay on 10 December 1982 and entered into force on 16 November 1994. ITLOS, “UNCLOS.”

[16] Iran and Oman, together with Spain, Morocco, Malaysia, Indonesia and South Yemen, were among the coastal states that resisted the non-suspendable transit-passage regime during the UNCLOS III negotiations. Lewis M. Alexander, “International Straits,” U.S. Naval War College International Law Studies, vol. 91.

[17] Iran signed UNCLOS in 1982 but has never ratified it, having specifically objected to the transit-passage regime as a “quid pro quo” bargain rather than customary law; it is accordingly not bound by the Convention as a treaty party. Diplomat Magazine (EU edition), “The Strait of Hormuz and International Law: Can Iran Restrict or Charge for Passage?” (24 July 2026); UNCLOSdebate.org.

[18] Roughly a fifth of global oil supply and about a fifth of global LNG trade transit the Strait of Hormuz. International Energy Agency, “Strait of Hormuz”; U.S. Energy Information Administration, “World Oil Transit Chokepoints.”

[19] In August 1946 the Soviet Union demanded joint Turkish-Soviet defence of the straits and revision of Montreux; Turkey’s refusal, backed by Washington, became a formative episode of the Truman Doctrine. MoneyWeek, “7 August 1946: Turkish Straits Crisis Reaches Its Climax”; GlobalSecurity.org, “Soviet Dispute with Turkey.”

[20] Iran’s Revolutionary Guard Corps began levying de facto transit fees of roughly $1.5–2 million per vessel, payable in Chinese yuan or cryptocurrency, from mid-March 2026, later formalised by Iran’s parliament as the “Strait of Hormuz Management Plan” (30–31 March 2026). Kurdistan24, “Iran Confirms Strait of Hormuz Tolls Now Operational”; Maritime Executive, “Iran’s IRGC Is Charging Millions in Cryptocurrency for Hormuz Transits.”

[21] Indonesia’s finance minister raised, then swiftly withdrew, the possibility of tolls on the Strait of Malacca in April 2026, amid Singaporean objections. Maritime Executive, “Indonesia Backs Away After Finance Minister Proposes Malacca Tolls”; Bloomberg, “Malacca Ship Tolls Divide Emerges Between Indonesia, Singapore” (22 April 2026).

[22] The Houthi movement declared a naval blockade of Saudi Arabia and moved to charge transit fees at Bab-el-Mandeb in July 2026. Al Jazeera, “Yemen’s Houthis Declare Naval Blockade of Saudi Arabia” (20 July 2026); Euronews, “Houthis to Copy Iran’s Hormuz Playbook with Red Sea Toll Plan” (29 July 2026).

[23] The 2026 Strait of Hormuz crisis began on 28 February 2026 with the outbreak of war between the United States, Israel and Iran. Wikipedia, “2026 Strait of Hormuz Crisis.”

[24] The United States imposed a naval blockade on Iran on 13 April 2026. USNI News, “U.S. Reinstates Naval Blockade in Strait of Hormuz” (13 July 2026).

[25] Islamabad Memorandum of Understanding Between the United States of America and the Islamic Republic of Iran, 17 June 2026, para. 5. Full text: The American Presidency Project, presidency.ucsb.edu.

[26] Secretary of State Marco Rubio: “No country is allowed to charge tolls or fees on an international waterway. That’s existing international law.” CNBC, “UN Maritime Agency Opposes Hormuz Transit Fees After Trump Demands Protection Money” (13 July 2026).

[27] President Trump announced a proposed 20% transit levy on 13 July 2026 and reversed the proposal the following day in favour of Gulf investment pledges. CNBC, “Trump Proposes 20% Toll on Cargo Through Strait of Hormuz” (13 July 2026); The National, “Trump Drops 20% Hormuz Toll in Favour of Deals with Gulf States” (14 July 2026).

[28] Oman, backed by other Gulf states, presented Iran with a proposal for a regional mechanism, modelled on the Strait of Malacca’s voluntary-contribution scheme, for the joint management of navigation, environmental protection and search-and-rescue services in the Strait; as of late July 2026 Iran had not formally responded. Arab News, “Oman Proposes Regional Mechanism with Voluntary Fees to Manage Strait of Hormuz”; The Times of Israel, “Oman Hands Iran Gulf-Backed Proposal for Joint Control over Hormuz” (28 July 2026).

[29] IMO Secretary-General Arsenio Domínguez stated there is “no legal basis” for imposing transit fees in the Strait of Hormuz. CNBC and U.S. News & World Report, 13 July 2026.

[30] Iran and Oman are reportedly close to a deal on a new maritime corridor through the Strait of Hormuz, distinct from existing shipping lanes, as of early August 2026. Al Jazeera, “Iran Says Negotiations with Oman over Strait of Hormuz in Final Stages” (2 August 2026).

[31] Tanker attacks resumed near Oman’s coast in late July 2026, and President Trump and Iranian officials traded accusations over whether ceasefire talks had resumed. CNN, “Trump Calls Iranian Leadership ‘Unbelievably Duplicitous’ After Tehran Denies Talks Resumed” (2–3 August 2026); ABC News, Iran live updates.

[32] Iran’s lead negotiator has said the strait will not return to its pre-war, fee-free status once the Islamabad memorandum’s sixty-day window lapses around 16 August 2026, and that Iran will charge “fees for services” rather than tolls. Newsweek, “Iran to Charge Fees on Strait of Hormuz Even after Deal”; Yahoo Finance, “Iran Says Strait of Hormuz Will Have ‘Fees,’ Not ‘Tolls’” (2026).