Executive summary

With a seemingly ongoing war between the USA-Israel and Iran, the

entire Gulf region is on edge – the situation continuing to evolve day

by day, even hour by hour. Iran has sought to internationalize the

conflict so that other countries will put pressure on the United States

and its ally to end their air and missile offensives, now nominally on

hold during a fragile ceasefire.

We remain, however, in the midst of a stand-off whose impacts will

affect virtually everyone, everywhere. I refer, or course, to the closure

of the Strait of Hormuz, that narrow, shallow, and uniquely vital

waterway that connects the Gulf to the open seas – and haunts the

minds of risk analysts.

In addition to people dying in countries that have little or nothing to

do with the conflict, devastating socioeconomic consequences are

spreading around the globe, and conditions can only get worse if the

current blockades continue.

As everyone now knows, much of the world’s oil and natural gas

supplies – as well as derivative fuel and petrochemical products –

ordinarily pass through the Strait, whether bound for Europe, India,

China, or other countries across the Far East. Shortages are already

apparent in products ranging from petrochemicals to polymers, from

jet fuel to fertilizer. Diverse industries worldwide are affected,

consumers face higher prices, and global food security is at risk.

The unfortunate targeting of oil and gas facilities in Qatar, Saudi

Arabia, Kuwait, the UAE, Oman and Bahrain means the risk to

energy infrastructure in the Gulf remains very high. Before the current

interruption, GCC energy products have been the lifeblood of the

global economy. They have helped spread economic opportunity

across the world, lifting millions out of poverty through affordable and

reliable energy.

Irrespective of what happens next – whether a peace deal is negotiated

or hostilities resume – the global misery caused by Iran’s closure of the

Strait demonstrates a clear need for long-term solutions that are solidly

rooted both in law and in fact.

There is an urgent need for durable solutions which necessitate

immediate dialogue and diplomacy. Whatever form this process takes,

it should be based on existing international legal provisions, upholding

the rights of all states involved.

The potential gains and benefits from securing freedom of passage far

outweigh any perceived ‘achievements’ of military action or the

ongoing disruption to free movement in the Strait of Hormuz.

Background

The original War of the Straits took place almost 700 years ago –

fought between the Republics of Venice and Genoa from 1350 to

1355. The third in a series of conflicts between the two major Italian

maritime republics, the war resulted from intense rivalry over access to

the Aegean Sea and Black Sea, revolving around a battle for control of

passage through the Bosphorus Straits, from which the conflict drew

its name.

The Battle of the Bosphorus in 1352 pitched the Genoese fleet against

those of the Venetians and their allies, with the Genoese prevailing in a

confused battle fought at night, during a storm. Since then, wars and

conflicts over strategically important straits have erupted on a regular

basis. (See Appendix for details of the world’s major straits.)

The Strait of Hormuz first acquired importance after World War II,

given the discoveries of oil in neighboring countries – namely Saudi

Arabia, Iran, Kuwait, Iraq, Qatar, Bahrain, UAE and Oman – and

became a crucial waterway following the Iran-Iraq War of the 1980s.

Significant too is the nearby strait of Bab-el-Mandeb, a narrow

chokepoint separating Yemen from the Horn of Africa.

Today, around 25% of the world’s oil and gas passes through Hormuz,

while Bab-el-Mandeb carries a further 12%. Any closure of important

straits like these will affect not only energy prices, but also global food

security.

During the Iran-Iraq conflict, a tanker war erupted with civilian ships

needing a military escort through Hormuz. In July 1987, President

Ronald Reagan approved the escorting and US-flagging of Kuwaiti

ships for free passage. In that war, considerable damage was caused by

air attacks, missile hits, and mines, to which the United States

responded with Operation Praying Mantis, striking Iranian naval

targets – one of the most important US naval battles since World War

II.

Around that time, aiming to ensure crude supply to the free world,

Saudi Arabia’s Aramco constructed its East-West Pipeline 2 – a 48-

inch diameter connection across the Arabian Peninsula to Yanbu on

the Red Sea coast. Later, the UAE launched a similar pipeline to

Fujairah on the Gulf of Oman, together with an oil terminal there, to

bypass the volatile Strait of Hormuz.

The Tanker War (1981-88)

Mentioned previously, the Tanker War of the 1980s – fought in the

Arabian Gulf and Strait of Hormuz – involved systematic attacks on

oil tankers and merchant shipping by both Iran and Iraq, aiming to

disrupt each other’s economies and weaken their capacity to sustain

the wider Iran-Iraq War.

The conflict was triggered when Iraqi aircraft began to strike tankers

carrying Iranian crude – including, in May 1982, an attack on a vessel

loading oil at Kharg Island, Iran’s main oil export terminal. These

attacks intensified in 1984 with the use of advanced weaponry, such as

French-supplied Exocet missiles.

Iran responded by broadening the conflict to include ships associated

with Iraq’s allies, particularly Gulf Arab states like Kuwait and Saudi

Arabia, which were financially supporting Iraq. Iranian forces, including the Islamic Revolutionary Guard Corps Navy, used small

boats, naval mines, and occasional missile strikes to target tankers in

the Gulf. Unlike Iraq, which focused mainly on Iranian shipping, Iran

adopted a more indiscriminate approach, attacking neutral vessels and

thereby internationalizing the conflict.

Iraq's aim in attacking Iranian shipping had indeed been to provoke

the Iranians to retaliate with extreme measures, such as closing the

Strait of Hormuz to all maritime traffic, thereby bringing about

foreign intervention against Iran; the United States had threatened

several times to intervene if the Strait of Hormuz were closed.

Both sides had declared ‘exclusion zones’, warning ships against

entering specific areas. Iraq declared the area around Iran’s Kharg

Island to be an exclusion zone; Iran aimed to exclude shipping from all

waters within 40 miles of its coast, instructing vessels headed for non-

Iranian ports to sail west of this line. As the war escalated, the Gulf

became increasingly dangerous for commercial shipping. Hundreds of

vessels were damaged or destroyed, and insurance rates for transit

skyrocketed. The threat to global oil supplies alarmed the major

powers and, in 1987, President Ronald Reagan ordered the United

States to intervene directly, reflagging Kuwaiti tankers under the

American flag and providing naval escorts through the Gulf.

One of the most controversial incidents of the Tanker War occurred in

1987 when the US Navy frigate USS Stark was struck by Iraqi

missiles, killing 37 sailors. Iraq claimed the attack was accidental,

highlighting the chaotic and dangerous nature of the conflict. The

widespread use of naval mines further intensified risks. Iranian mine-

laying outpaced US minesweeping and proved to be the biggest hurdle

in international efforts to ensure the flow of oil to the rest of the world.

By 1988, however, both Iran and Iraq were exhausted economically

and militarily. The Tanker War had failed to decisively cripple either side’s oil exports but had drawn international forces into the conflict

and heightened global tensions. The war concluded shortly after Iran

accepted a UN-brokered ceasefire in August 1988.

The Hormuz chokepoint

The significance of energy transit chokepoints through narrow

channels cannot be overstated. As half of the world’s crude oil supplies

– and all its liquefied natural gas (LNG) – relies on maritime

transportation, protecting the free flow of oil and gas through shipping

routes is crucial for energy price stability worldwide, as well as the

reliability of supply.

If we consider just the passage of hydrocarbons through the Strait of

Hormuz, at April 2026 prices, the value of exports from countries

adjacent to the Gulf is more than half a trillion dollars a year. The

world economy cannot afford such a closure.

For decades, the Iranian government has claimed the right, boasted

the ability, and vowed a willingness to close this waterway in response

to various forms of military or other pressure from the United States.

About a fifth of the world's oil transits this passage. For good measure,

Hormuz is also the route by which some 200 million people, including

most of the six-nation Gulf Cooperation Council (GCC), receive the

majority of their food and other imports.

Outwardly, Iranian officials have denied targeting GCC countries and

other states with missiles and drones, insisting that their forces were

aiming instead at US military assets on their soil, even though most of

these countries have not allowed their airspace to be used for the US-

Israeli offensive.

Even if it were true, the Iranian interpretation would certainly be a

distinction without a difference for those mourning lost loved ones, but

there have now been countless attacks drone and missile attacks on

homes and residential buildings, port facilities, oil and gas

infrastructure, and other civilian targets in several GCC countries. The

Iranians seem to have calculated that inflicting some degree of pain on

their neighbours will cause more voices – in this case from within US-

allied countries – to demand a permanent end to the war.

The arithmetic of exports and imports makes Hormuz the world's

ultimate chokepoint. The mere possibility of lasting disruption there

has caused energy prices to rise on countless occasions, including the

current crisis, and an actual closure for any length of time would be

highly corrosive to the global economy. And since energy prices are

baked into virtually everything else, the pain would be felt almost

everywhere.

This Hormuz case study addresses the legal regime of the Strait of

Hormuz as applicable to the Islamic Republic of Iran (Iran) and the

Sultanate of Oman (Oman), being the coastal States bordering the

Strait of Hormuz (‘Strait states’), as well as countries using the Strait of

Hormuz (‘user states’), including merchant vessels flying the flag of

user states, under the international Law of the Sea. The rights of

merchant vessels transiting the Strait of Hormuz are linked to the flag

under which they are registered.

For this reason, it must be established: (i) what legal regime applies to

the individual flag state concerned, and (ii) what maritime zone is

involved. The Law of the Sea makes a basic distinction between a

coastal State’s territorial waters, a belt of sea of up to 12 nautical miles

(nm) from their coastline and in which the coastal State has full

sovereignty, and maritime zones beyond the territorial sea, where a

coastal state enjoys more limited sovereign rights, not sovereignty. This

affects the Strait passage regime. From a legal perspective, the current situation in the Strait of Hormuz

is complicated by the applicability of both the law of international

armed conflict at sea (jus ad bellum or the laws of war, including naval

warfare) and the Law of the Sea, including rules governing

international navigation through straits. The belligerent states in the

present conflict (Iran, Israel, and the United States) are not parties to

the United Nations Convention on the Law of the Sea (UNCLOS),

which was concluded in 1982 and entered into force in 1994. They

have not ratified the UNCLOS. This means that the rules included in

that treaty are not binding on them as treaty law.

The law of armed conflict imposes special rules on the use of force,

which is lawful only in a situation of “self-defense if an armed attack

occurs against a member of the United Nations” (Article 51 of the UN

Charter) or following authorization by the UN Security Council. The

International Court of Justice (ICJ), the principal judicial organ of the

United Nations, has taken the position that international law requires

proof of a specific intention of a state to attack a particular target, to

trigger an “armed attack” permitting the use of force in responsive

self-defense, including proof that the attack in question can be

attributed to the accused state, such as through the actions of its armed

forces. (Oil Platforms [Iran v. USA], Judgment, ICJ Reports 2003, p.

191.)

Under the laws of war, a state using force in exercise of its inherent

right of self-defense (including by firing missiles at ships or by laying

submarine mines targeting ships) may have the right to use force also

against foreign-flagged merchant vessels carrying cargo that can be

proven to be in transit to an attacking state, or which are transiting

through an international strait while being escorted by warships of a

belligerent state (here, the United States and Israel, the two countries

that initially used force against Iran, triggering the current armed

15

conflict), based on the theory that such vessels have become legitimate

military objects as “enemy” merchant vessels.

Iran’s recent actions in the Strait of Hormuz do not (yet) amount to an

effective “naval blockade” as this term is understood in international

law. In the absence of an effective naval blockade, whatever strait

passage regime applies in principle will continue to apply during an

international armed conflict.

The Strait of Hormuz connects the Gulf of Oman, the Arabian Sea

and the Indian Ocean with the Arabian Gulf. The coastal states

bordering the Strait of Hormuz are Iran (to the north) and Oman (to

the south), while the approaches to the Strait of Hormuz in the

Arabian Sea (to the east) and the Arabian Gulf (to the west) also

involve the maritime zones of the United Arab Emirates (UAE). An

indication of the outer limits of the Strait of Hormuz can be derived

from the “Agreement concerning the Delimitation of the Continental

Shelf between Iran and Oman” concluded in July 1974 and fully in

force. Through that treaty, the two Strait states agreed a boundary line

delimiting the continental shelf between their territories. The 1974

treaty does not refer to the territorial sea of either country; it only

delimits their continental shelf boundary.

A so-called Traffic Separation Scheme (TSS) is in force in the Strait of

Hormuz. It was originally adopted by the Inter-Governmental

Maritime Consultative Organization (IMCO) in November 1973 and

was modified by the International Maritime Organization (IMO),

IMCO’s successor, in June 1979. The TSS in the Strait of Hormuz

comprises inter alia a separation zone and two traffic lanes for,

respectively, westbound and eastbound traffic in the Strait. These

special sea lanes are mandatory for merchant vessels transiting the

Strait of Hormuz. Iran and Oman are both IMO member states and

as such must respect the IMO-mandated shipping lanes in the Strait of

Hormuz.

16

The UNCLOS includes specific provisions concerning the legal

regime of straits used for international navigation in Part III, which is

not limited to straits as territorial seas. However, Iran has signed but

not ratified the UNCLOS, which means that the UNCLOS provisions

and rules are not opposable to Iran as treaty law. The same applies to

the UAE. Oman has ratified the UNCLOS and so have Panama and

the People’s Republic of China, both user states and prominent flag

states. The USA, another user state, has not ratified the UNCLOS.

Under the international law of treaties, as codified in the 1969 Vienna

Convention on the Law of Treaties, a state that has signed but not

ratified a treaty is obligated to refrain from acts that would defeat the

object and purpose of a treaty that it has signed, pending the

ratification process. This rule, which is codified in Article 18 of the

1969 Vienna Convention, is widely considered as declaratory of

customary international law, meaning it also is binding on a country

that has not ratified the Vienna Convention (in the absence of a

consistent objection). Iran has signed but not ratified the Vienna

Convention.

The right of “transit passage” applicable to a strait that meets the

definition under UNCLOS Article 37 is more liberal and stronger

than the right of “innocent passage” applicable to a coastal state’s

territorial sea in general. Article 38(2) of the UNCLOS defines transit

passage as “the exercise in accordance with this Part [III] of the

freedom of navigation and overflight solely for the purpose of

continuous and expeditious transit of the strait between one part of the

high seas or an exclusive economic zone, and another part of the high

seas or an exclusive economic zone”. The same provision makes clear

that “the requirement of continuous and expeditious transit does not

preclude passage through the strait for the purpose of entering, leaving

or returning from a state bordering the strait, subject to the conditions

of entry to that state”.

According to Article 34 (1) of the UNCLOS, “the regime of passage

through straits used for international navigation established in this Part

[III] shall not in other respects affect the legal status of the waters

forming such straits or the exercise by the States bordering the straits

of their sovereignty or sovereign rights over such waters and their air

space, bed and subsoil”. In other words, the UNCLOS strait transit

regime is not restricted to the territorial sea of a coastal state.

Article 39 of the UNCLOS spells out the duties of ships during transit

passage, including to “proceed without delay through...the strait.”

Article 44 of the UNCLOS includes a treaty obligation for coastal

states bordering straits not to hamper transit passage in any way. The

same provision stipulates that “there shall be no suspension of transit

passage” in an Article 37 strait by states bordering such a strait. Unlike

the right of “innocent passage” through a coastal state’s territorial sea

in general (discussed below), suspension of the exercise of the right of

transit passage in territorial sea straits is hence unlawful under the

UNCLOS.

Therefore, the applicable legal regime regarding strait passage

depends on whether a given state is a party to the UNCLOS, having

signed and ratified that treaty, or whether it is subject to customary

international law in the absence of a treaty that is applicable to that

state. According to Iran, the UNCLOS regime of transit passage

applies only to states having ratified the UNCLOS; this regime does

not apply to non-ratifying states that have objected to the right of

transit passage, such as Iran, and the right to transit passage does not

reflect customary international law. In contrast, the position of the

United States is that the UNCLOS transit passage regime reflects

customary international law, meaning it also applies to non-ratifying

states unless they have consistently objected to it.

For states party to the UNCLOS, including Oman, Article 37 “applies

to straits which are used for international navigation between one part

of the high seas or an exclusive economic zone, and another part of

the high seas or an exclusive economic zone.” The Strait of Hormuz

fits this definition which, as earlier noted, is not limited to straits as

territorial seas. For Article 37 straits, the regime of “transit passage”

applies. Thus, the Strait of Hormuz is a “transit passage” strait for

states party to the UNCLOS, including both Oman as a Strait state

and user states such as Panama and the People’s Republic of China.