BP carries out oil well test before 'top kill' bid

Environmentalists are concerned for the welfare of coastal birds and sealife

The oil company BP is carrying out diagnostic tests to ensure a plan to plug the leaking Gulf of Mexico oil well does not backfire.

A senior BP vice president, Kent Wells, said on Tuesday scientists would run the tests "over the next day or so".

If the "top kill" procedure is used, heavy drilling fluids will be injected into the well about a mile (1.5km) underwater.

BP is under intense pressure to succeed after previous measures failed

The BP-leased well began leaking through its riser pipe after the explosion of a drilling rig, the Deepwater Horizon, on 20 April with the loss of 11 lives.

A conservative estimate of the amount of oil escaping is about 5,000 barrels (210,000 gallons, 795,000 litres) a day while some scientists say it could be many times greater.

The US government has declared a "fishery disaster" in the seafood-producing states of Louisiana, Mississippi and Alabama.

President Barack Obama is due to make his second visit to the Gulf of Mexico region on Friday.

Aides quoted him as telling senior government officials: "Plug the damn hole."

'Crucial tests' Ultra-deepwater rigs and other equipment are at the site

Oil industry experts quoted by Reuters news agency gave the "top kill" procedure a 50-50 chance of working.

Mr Wells estimated a 60%-70% chance of success.

"This has been done successfully all over the world but it has never been done 5,000 feet below the surface of the sea," he said.

US Energy Secretary Steven Chu has been monitoring the preparations and told Mr Obama in a phone briefing that BP was conducting "crucial diagnostic pressure tests" before proceeding.

In the tests which began on Tuesday, five spots on the well's crippled five-story blowout preventer were being checked to make sure it could withstand the heavy force of the injection.

A weak spot in the device could blow under the pressure, causing a brand new leak.

"When the actual kill might go forward, the earliest might be tomorrow and that could extend on from there," Mr Wells said on Tuesday.

"We have to be careful in terms of setting expectations," he added.

BP has been drafting plans for the "top kill" for weeks but had to delay it several times as crews scrambled to assemble the equipment at the site 50 miles (80km) off the Louisiana coast.

Rigs, barges and other heavy machinery stood at the ready on Tuesday.

If the procedure goes ahead, it will be streamed on live video.