The Persian Gulf and the Strait of Hormuz
The Persian Gulf is the inland sea between Iran and the Arabian Peninsula, opening to the Gulf of Oman through the Strait of Hormuz.
The Persian Gulf is the inland sea between Iran and the Arabian Peninsula, opening to the Gulf of Oman through the Strait of Hormuz. Some of the largest oil and gas fields in the world lie around this shallow water, and Hormuz is its only way out to the ocean. In 2024 an average of 20 million barrels of oil a day passed through the strait.[4] Since the Iran war began on 28 February 2026 that traffic has been badly disrupted, and at the start of November 2026 it had still not returned to normal.
A Shallow Inland Sea
The Gulf covers about 251,000 square kilometres and runs 989 kilometres from the Shatt al-Arab delta in the northwest to Hormuz. It averages 50 metres deep and reaches about 90 metres at its deepest. In a hot, dry climate evaporation is high, so the water is saltier than the open ocean. Dense salty water leaves along the bottom while less salty water comes in at the surface.[3] The coastal states are Iran, Iraq, Kuwait, Saudi Arabia, Bahrain, Qatar, the United Arab Emirates and, through its Musandam territory, Oman.
Shallow depth and slow water exchange leave the sea vulnerable to pollution. Coral, seagrass and pearl beds all suffer from coastal reclamation, desalination discharge and oil spills. Oil spilled in the 1991 Gulf War left its mark on the seagrass and on the dugongs that feed there.[3]
Even the name is contested. Persian Gulf is the historical and international name. Arab governments have mostly said Arabian Gulf, or simply the Gulf, since the 1960s.[3]
Pearls, the Portuguese and the British
Before oil, the wealth of the Gulf lay on its seabed as pearls. The Portuguese entered Bahrain in 1521 in pursuit of that income.[3] Divers stayed at sea for months each summer, while dry cargo moved in wooden boats between India and East Africa. The dhows still waiting for cargo on Dubai Creek carry on that trade.
The British came because of the India trade. A first clash with Al Qasimi vessels took place in 1797, and London treated raiding on this coast as a threat to the route to India. After expeditions in 1809 and 1819, the coastal sheikhs signed the General Maritime Treaty with Britain on 8 January 1820. A perpetual maritime truce followed on 4 May 1853. In 1892 the sheikhs signed exclusive agreements leaving their foreign relations to Britain, partly because of French and Russian interest in the region. The coast became known as the Trucial States.[14]
The First Oil, on the Iranian Side
The first big discovery in the region came in Iran. In May 1901 the British investor William Knox D'Arcy paid the Shah £20,000 for a 60-year concession covering Persia outside its northern provinces. He never visited the country himself. By January 1904 he had spent £160,000 and was overdrawn at his bank by £177,000, so in 1905 he brought in Burmah Oil as a backer. In April 1908 the partners decided to give up, but the drilling engineer on site, George Reynolds, delayed carrying out the order. On 26 May 1908 he struck oil at Masjed Soleyman at a depth of about 360 metres. The Anglo-Persian Oil Company was formed in April 1909, and by 1911 a pipeline linked the wells to the Abadan refinery.[13]
Frank Holmes and Bahrain
The search on the southern shore began with the persistence of one New Zealander. Frank Holmes was born in 1874, went at 17 to work as an apprentice at a gold mine in southern Africa, and spent two decades as a mining engineer in gold and tin. In the First World War he served as a British Army quartermaster sourcing supplies for Mesopotamia, which took him around the Middle East. In 1918 he wrote to his wife that he expected a very large oil field running from Kuwait.[11] In 1920 he helped set up the Eastern and General Syndicate in London and went looking for concessions.
Ibn Saud gave him a concession for the al-Hasa region in 1923, but a later survey was unfavourable, no buyer came forward and the concession lapsed. In Bahrain, Holmes tried a different approach. He offered the sheikh water wells, and in exchange on 2 December 1925 he had his oil concession.[11][12] The syndicate could not pay for drilling and had to sell. Gulf Oil bought an option on 30 November 1927, but the Red Line Agreement it had signed with its Iraq Petroleum partners stopped it from working Bahrain alone. So on 21 December 1928 Gulf passed the option to Standard Oil of California for $50,000. That company set up the Bahrein Petroleum Company (Bapco) in Canada in January 1929.[12]
Drilling began at the foot of Jebel Dukhan, and oil came on 2 June 1932. Bapco's own record gives a flow of 400 barrels an hour, while another account of the same well gives about 2,400 barrels a day.[1][12] The island's old livelihood was collapsing at the same time, as cheap cultured pearls from Japan destroyed the pearl trade.[2] The first crude shipment left the Sitra terminal on 7 June 1934 aboard the tanker El Segundo, also bound for Japan, with 25,000 barrels on board. The refinery opened in December 1937.[1]
After Bahrain, attention turned across the water. The Kuwait Oil Company, formed by Holmes's group and Anglo-Persian, won a 75-year concession on 23 December 1934 and struck oil at Burgan in February 1938. Standard Oil of California took the Saudi concession and found oil at Dammam the same year.[11] The war slowed development, then in the 1950s the industry's centre of gravity moved to the Gulf. Aramco found Safaniya, regarded as the largest offshore field in the world, in 1951. Shallow water helped here, because platforms were comparatively easy to build far from shore. The North Field, found in 1971, forms with Iran's South Pars the largest gas field in the world, and it made Qatar a leading LNG exporter.[3]
The British Withdrawal and 1973
As oil income grew, the British order in the region neared its end. On 16 January 1968 London announced it would withdraw from east of Suez, and the withdrawal was completed on 30 November 1971. A day earlier Iran had landed on Abu Musa and the Greater and Lesser Tunbs, islands close to Hormuz. On 2 December six sheikhdoms formed the United Arab Emirates.[14] The political weight of Gulf oil showed itself two years later in the 1973 crisis.
The Tanker War
Tankers first became targets in the Iran-Iraq War. The two countries went to war in 1980 and the naval side began in 1981. It escalated in 1984 when Iraq struck the Kharg Island terminal and tankers, aiming at Iran's oil exports. Between 1981 and 4 August 1988, Iraq carried out 283 attacks and Iran 168. Well over a hundred seafarers died and about as many were wounded.[5]
Kuwait backed Iraq, and its tankers came under Iranian attack too. In January 1987 it proposed putting its ships under the US flag and US Navy protection, and Washington agreed on 7 March. On 17 May an Iraqi aircraft hit USS Stark and killed 37 American sailors, and Saddam Hussein apologised, saying the pilot had taken the ship for an Iranian tanker. The Earnest Will convoys began on 24 July 1987, and on the very first run the US-flagged Bridgeton struck an Iranian mine. In April 1988 the US Navy attacked Iranian forces.[5]
Hormuz and the Limited Routes Overland
The importance of the strait is a matter of plain geography. Hormuz is about 33 kilometres wide at its narrowest and the traffic lanes occupy a small part of that. On US Energy Information Administration figures for 2024, the 20 million barrels a day through the strait equalled about a fifth of world consumption and more than a quarter of seaborne oil. Saudi Arabia supplied 38% of the crude and condensate, or 5.5 million barrels a day, and 84% of the flow went to Asia. About a fifth of global LNG trade, mostly from Qatar, took the same route.[4]
There are few ways around it. Saudi Arabia's East-West line from Abqaiq to Yanbu on the Red Sea carries 5 million barrels a day and was temporarily raised to 7 million in 2019. The UAE's Fujairah line has a capacity of 1.8 million barrels. The EIA put spare capacity on these two lines at about 2.6 million barrels a day in a crisis.[4] Iraq's northern Kirkuk-Ceyhan line stopped in March 2023 and restarted in September 2025. In March 2026 it was exporting 250,000 barrels a day, against normal Iraqi exports of 3.5 million.[18] Qatar's LNG has no such alternative. The pipeline transport article covers these lines in more detail.
The 2026 War and the Closure
The United States and Israel launched hundreds of air strikes on Iran on 28 February 2026, during nuclear talks, killing Supreme Leader Ali Khamenei.[16] Within hours the Revolutionary Guards were telling ships by radio that none could pass, and traffic fell by about 70%. On 1 March the tanker Skylight was hit and two of its crew were killed. On 5 March protection and indemnity cover was withdrawn, leaving the strait legally open and effectively closed.[15] In its March report the International Energy Agency said at least 10 million barrels a day of supply was out of action and more than 3 million barrels a day of Gulf refining capacity had stopped, calling it the largest disruption in the history of the oil market. Members agreed on 11 March to release 400 million barrels from stocks.[6] On 21 April the IMO reported about 2,000 ships and 20,000 seafarers stranded in the Gulf.[15]
A Pakistani-brokered ceasefire came on 8 April, but the Islamabad talks failed and the US Navy began blockading Iranian ports on 13 April. On 17 April Iran said it would open the strait to commercial ships, then reimposed restrictions when the blockade continued.[15][16] Tehran had meanwhile come to see passage as a source of revenue. It had announced in March that ships must pay for safe transit, and on 5 May it created the Persian Gulf Strait Authority to issue permits. The US Treasury had warned on 1 May that paying could bring sanctions exposure.[17]
In June a settlement looked close. The Islamabad Memorandum, meant to end the war and the rival blockades, was signed on 17 June. Three days later Iran said it had closed the strait again, citing Israeli strikes in Lebanon. On 8 July the truce collapsed after Iran hit several commercial ships, and the United States reinstated its blockade on 14 July. On 25 August US officials confirmed that the traffic separation scheme, where more than 100 suspected mines had been identified, was clear.[15]
The Picture in Autumn 2026
With the war still going on, oil began to move by another method. The UAE, Saudi Arabia and Kuwait run their own tankers through the strait in convoys, transfer the cargo to ships waiting outside and go back to load again. Many tankers switch off their tracking signals, which makes counting very hard. Kpler put Gulf crude and condensate flows at 24.6 million barrels a day in the week to 18 October, while Vortexa gave 18 million for the same week. The averages for October to that date were 16.7 and 15.4 million respectively, against a pre-war level of at least 18.5 million.[8]
Ship counts diverge in the same way. Lloyd's List Intelligence recorded 104 transits by vessels with no Iranian link in the week of 5 to 11 October. IMF PortWatch's pre-war reference was about 85 transits a day, and its data showed just 2 for 25 October.[7][10] The methods differ, so the figures cannot be added together. The violence is getting worse. UKMTO reported 32 attacks on ships around the Arabian Peninsula in the first three weeks of October, against 16 in all of September.[8] The US blockade had redirected 138 merchant ships, and Iran's blacklist had grown to 124 vessels.[7] Incident records for 1 March to 1 November list 104 attacks and the deaths of 24 seafarers and a port worker. Talks continue, and Qatari mediators hosted Iranian officials in Doha on 30 October.[15]
In the bunker market Fujairah took the hardest hit. This port outside the strait, on the Gulf of Oman, was the largest bunkering hub in the Middle East. Sales in the first nine months of 2026 fell to 2.35 million cubic metres, down 58% from 5.60 million a year earlier. September sales were 236,735 cubic metres, 62.9% below September 2025.[9] For an owner reworking freight and fuel plans around the route, the choice of bunker port in this region now depends on war risk. Other supply points are listed on the ports page.
Frequently asked questions
Where is the Persian Gulf?
The Persian Gulf is the inland sea between Iran and the Arabian Peninsula, opening to the Gulf of Oman through the Strait of Hormuz.
Which countries border the Persian Gulf?
Iran, Iraq, Kuwait, Saudi Arabia, Bahrain, Qatar and the United Arab Emirates, plus Oman through its Musandam territory.
How wide is the Strait of Hormuz?
About 33 kilometres at its narrowest. The traffic lanes used by ships take up a small part of that width.
Is the Strait of Hormuz open?
At the start of November 2026 the strait had not returned to normal operation. Some tankers pass in convoys, often with tracking switched off, attacks continue and the US blockade of Iranian ports remains in place.
Sources
- Bapco. History timeline.
- Bahrain This Month. The History of Pearling in Bahrain.
- Wikipedia. Persian Gulf (secondary source).
- US Energy Information Administration (EIA). Amid regional conflict, the Strait of Hormuz remains critical oil chokepoint, 16 June 2025.
- Wikipedia. Tanker war (secondary source).
- gCaptain. IEA Warns Hormuz Crisis Triggering Largest Oil Supply Disruption in History, 12 March 2026.
- Lloyd's List Intelligence. Strait of Hormuz Brief, 22 October 2026.
- gCaptain and Bloomberg. Middle East Oil Flows Near Prewar Levels, Defy Hormuz Attacks, 21 October 2026.
- Ship & Bunker. Fujairah Bunker Sales Recover Some but Remain More Than Half Below Last Year, 2026.
- straits.live. Daily Hormuz brief, 3 November 2026 (IMF PortWatch data).
- Wikipedia. Frank Holmes (geologist) (secondary source).
- Wikipedia. Bahrain Petroleum Company (secondary source).
- Wikipedia. William Knox D'Arcy (secondary source).
- Wikipedia. Trucial States (secondary source).
- Wikipedia. 2026 Strait of Hormuz crisis (secondary source).
- Wikipedia. 2026 Iran war (secondary source).
- Wikipedia. Persian Gulf Strait Authority (secondary source).
- Wikipedia. Kirkuk-Ceyhan Oil Pipeline (secondary source).
