Gulf of Mexico: Leak in oil well capped

The most ambitious attempt yet to halt the oil gushing from the floor of the Gulf of Mexico was underway as a new, tight-fitting cap was successfully placed on the damaged wellhead, oil company BP Plc's undersea video feed showed.

US Coast Guard Admiral Thad Allen, the presidentially appointed national incident commander, said "significant progress has been made" in the so-called capping stack installation, which contains a series of valves and was installed late on Monday.

Starting early on Tuesday, BP engineers plan to begin closing the new valves, gradually raising pressure in the well, Allen said. The tests are intended to show if the wellhead is able to withstand the pressure of a complete or partial shutdown.

If not, the new cap should at least allow much improved collection of oil from the leaking well.

The tests could take from 6 to 48 hours or more, Allen said.

Meanwhile, BP is drilling a relief well that it hopes would intersect the existing well shaft next month, allowing a permanent closure of the well.

The leak has spewed massive undersea pollution for three months and caused oil to wash up in nearby Louisiana and other states on the eastern Gulf Coast.

The US government on Monday took another stab at suspending deepwater oil drilling even as it defended an earlier moratorium that was overturned last month by a federal judge.

US Interior Secretary Kenneth Salazar ordered a new, six-month suspension of deepwater drilling aimed at preventing another leak.

The order makes minor changes to a May 27 moratorium, by allowing some operations to resume if companies demonstrate they can do so safely.

It also lifted earlier depth restrictions. The first moratorium, contested in court by oil companies and operators, only applied to wells at depths greater than 150 meters.

Shallow water operations could continue because they use different, safer technology, the government said.

"I am basing my decision on evidence that grows every day of the industry's inability in the deepwater to contain a catastrophic blowout, respond to an oil spill and to operate safely," Salazar said.

The newest moratorium brought protests from the American Petroleum Institute, which warned it would cost jobs and "weaken our nation's energy security".

It said 33 deepwater drilling rigs in the Gulf of Mexico were sitting idle even though they passed government inspections.

At the leak site, BP was aiming for the 5-metre, 75-tonne cylinder newly installed atop the well to funnel all of the estimated 30,000 to 60,000 barrels of oil leaking daily up to tanker ships.

"You can think of it as this great big faucet that we're going to slowly crank down and turn off the flow and then check the pressure over a period of time," BP spokesman Steve Rinehart told The Washington Post.

If the pressure climbs, BP engineers were optimistic they could capture the entire outflow. But flat or low pressure would be a bad sign.

"If the pressure were lower, it could mean the oil is escaping somewhere else," said Doug Suttles , who oversees oil exploration for BP.

Since April, a series of attempts by BP to contain the oil flow have failed, amid the complexity of fixing a ruptured wellhead at unprecedented ocean depths.

The Deepwater Horizon rig, which exploded April 20 and killed 11 workers had drilled a well estimated to stretch at least 4,500 metres beneath the wellhead on the seafloor, which is 1,500 metres below the sea surface.