Analysis: Threats to Middle East Shipping

Warplanes from Saudi Arabia and Arab allies struck Shi'ite Muslim rebels fighting to oust Yemen's president on Thursday, in a push by the world's top oil exporter to check Iranian influence in its backyard.

Earlier air strikes south of the city and in the oil-producing Marib region appeared to target military installations also affiliated with Saleh.

Yemeni oil flows through the Marib pipeline, its main export route, at a rate of around 70,000 barrels per day (bpd). The well-armed tribes are the de facto authority in the central province, so their support for the air strikes was significant.

Warplanes also hit two districts in the Houthis' northerly home province of Saada, tribal sources said. The strikes hit a market in Kataf al-Bokaa in the north of Saada, killing or wounding 15 people, they said. Shada district was also struck.

Below are facts about threats to the major energy transit routes of the Middle East and possible alternative routes.

Strait of Hormuz

The Strait of Hormuz is the most important oil transit channel in the world, with some 17 million barrels per day (bpd), or about 30 percent of all seaborne-traded oil, passing through in 2013, according to the U.S. Energy Information Administration (EIA).

Most of the crude exported from Saudi Arabia, Iran, the United Arab Emirates (UAE), Kuwait and Iraq -- together with nearly all the liquefied natural gas (LNG) from lead exporter Qatar -- must slip through a four-mile-wide (6.4 kilometer) channel between Oman and Iran.

More than 85 percent of the crude oil that moves through it is sent to Asia -- mainly Japan, India, South Korea and China.

The U.S. Fifth Fleet, based in Bahrain and responsible for an area that includes the Gulf, Red Sea, Gulf of Oman and parts of the Indian Ocean, said it would not allow any disruption of traffic in the Strait of Hormuz.

Saudi Arabia

Saudi Arabia has exported most of its crude on tankers passing through the Strait of Hormuz.

Its other operational pipeline route is the Petroline, or "East-West Pipeline," which mainly transports crude from fields clustered in the east to the Red Sea port of Yanbu for export to Europe and North America.

The 5 million bpd Petroline could transport around 60 percent of total Saudi oil exports, which can get close to 8 million bpd. But it is already used for supplying markets west of the Suez Canal, leaving less than 5 million bpd of spare capacity for fuel looking for another way out of the Gulf.

Around two-thirds of Saudi crude exports go to Asia, so pumping it west and then shipping it east means tankers would also have to sail through the pirate-infested Bab el-Mandeb Strait and Gulf of Aden on a voyage that is about 1,200 miles and five days longer.

A parallel 290,000 bpd Abqaiq-Yanbu natural gas liquids (NGL) pipeline links gas processing plants in the east with NGL export facilities at Yanbu. But it too provides only a partial alternative to Saudi shipments of NGL from the Gulf.

In 2012, Saudi Arabia reopened an old oil pipeline built by Iraq -- the 1.6 million bpd Iraqi Pipeline in Saudi Arabia (IPSA) -- to bypass Gulf shipping lanes.

Other Gulf Producers

Other OPEC members, Iran, the UAE, Kuwait, and Qatar currently rely entirely on the Strait of Hormuz.

But the UAE has built a new pipeline -- Abu Dhabi Crude Oil Pipeline with a capacity of 1.5 million bpd -- to carry the bulk of its production to Fujairah, a bunkering hub and an oil terminal bypassing the Strait.

Qatar, a small crude exporter, shipped about 3.7 trillion cubic feet (tcf) per year of LNG through the Strait of Hormuz in 2013, according to BP Statistics.

Iraq

Nearly 80 percent of Iraq's crude is exported through Gulf ports, mostly to Asia. It pumps around 400,000 bpd via a northern pipeline through its Kurdistan region to the Turkish port of Ceyhan, since the existing 1.5 million bpd northern pipeline has been dogged by a series of bombings and disruption.

Iran

Iran's total reliance on crude exports through Hormuz is one of the reasons why it is unlikely to be blocked.

Suez Canal/SUMED

The Suez Canal and SUMED Pipeline are strategic routes for Mideast oil and natural gas shipments to Europe and North America. These two routes combined accounted for about 8 percent of the world's seaborne oil trade in 2013, according to the EIA.

In 2013, nearly 3.2 million bpd of total crude oil and refined products transited the Suez Canal in both directions, according to the Suez Canal Authority.

In 2013, 1.4 million bpd of crude oil was transported through the SUMED Pipeline.

LNG flows through the Suez Canal in both directions were 1.2 tcf in 2013, around 10 percent of total LNG traded worldwide.

Bab el-Mandeb Strait

A blockage of the two-mile wide shipping lane between unstable Yemen and mainland Africa would render both the Suez Canal and SUMED nearly redundant.

The U.S. EIA estimates more than 3.4 bpd of oil passed through the narrow, pirate-infested channel in 2013. Its closure would force oil and LNG tankers to sail around the southern tip of Africa, tying up tankers for weeks and driving up costs.