In this graphic, black regions show the forecast extent of oil, while the uncertainty boundary represents the maximum possible span of the leak in the Gulf. (CBC)

BP said Wednesday it hopes to begin shooting a mixture known as drilling mud into the blown-out well in the Gulf of Mexico early next week.

Engineers hope to start the procedure known as a "top-kill" by Sunday. It could take several weeks to complete, but if it works it should stop the oil that's been gushing since the offshore drilling rig Deepwater Horizon exploded off the coast of Louisiana on April 20 and sank two days later.

"This is all being done at a depth of 5,000 feet and it's never been done at these depths before," said Doug Suttles of BP, the oil giant that was leasing the rig when it exploded.

Meanwhile, scientists with the European Space Agency said the spill has entered a powerful current that could draw the oil beyond the Gulf into the Florida Keys and up the Atlantic Coast.

BP America Inc. president Lamar McKay, left, and Transocean Ltd. CEO Steven Newman, right, testify during a U.S. Senate committee hearing in Washington on Tuesday. (Manuel Balce Ceneta/Associated Press)

The scientists used radar satellite to track the spill into the Loop Current, named because it flows clockwise around the Gulf of Mexico, the ESA said.

"With these images from space, we have visible proof that at least oil from the surface of the water has reached the current," said Dr. Bertrand Chapron, of the French Research Institute for Exploitation of the Sea.

U.S. government scientists were also surveying the Gulf to determine if the oil had reached the current.

U.S. and Cuban officials held "working level" talks on how to respond should the current carry the slick to the pristine white beaches along Cuba's northern coast.

"It is incumbent upon us to inform all of our neighbours, not just the islands, but those countries that could be affected by disasters that happen within our territorial waters," State Department spokesman Gordon Duguid told reporters in Washington.

Oil could spell disaster for wildlife and vegetation along Florida's coastline and damage the state's tourism industry.

Laboratory tests showed more than two dozen tar balls found Monday and Tuesday on a beach in the Florida Keys don't match the type of oil in the Gulf spill, the U.S. Coast Guard said Wednesday.

The source of the tar balls isn't known. They can occur naturally or come from other sources such as ships.

BP, Transocean defend practices

In Washington, far from the oil spill, BP and Transocean officials once again defended their company practices at a U.S. congressional committee examining the oil spill in the Gulf of Mexico.

House transportation and infrastructure committee member Representative John Mica, of Florida, blamed the Gulf of Mexico oil spill on the Obama administration's lax regulations at a hearing Wednesday in Washington. (Lawrence Jackson/Associated Press)

BP America CEO Lamar McKay and Steven Newman, the CEO of Transocean Ltd., appeared side by side Wednesday before the House transportation and infrastructure committee.

Similar hearings last week before different committees resulted in what President Barack Obama called a "ridiculous spectacle" in which the executives appeared to be "falling over each other to point the finger of blame at somebody else."

This time, the executives whose companies are being investigated for the devastating spill showed slightly more contrition.

"There is a deep and steadfast resolve to do all we humanly can to stop this leak, contain the spill and minimize the damage," McKay testified.

"Ours is an industry that must put safety first," Newman said.

Pinning blame on Obama

Instead, the finger pointing Wednesday was done primarily by Representative John Mica, a Florida Republican, who sought to pin blame for the disaster on Obama's administration.

A video taken by a remotely operated vehicle on Saturday shows one of two oil leaks in a bent riser pipe still attached to the blowout preventer at the top of the seabed wellhead. (BP)

Outlining what he called the "Obama oil spill timeline," Mica said the administration failed to heed warnings about the need for more regulation.

He said it also issued "basically a carte blanche recipe for disaster" in approving drilling by the Deepwater Horizon, leased from Transocean by oil giant BP PLC, and several dozen other wells.

"I'm not going to point fingers at BP, the private industry, when it's government's responsibility to set the standards," he said.

As for BP's preparedness to deal with potential safety failures, McKay stressed many times that the current spill is "an extremely unique situation" that could not have been foreseen.

Leaks in a riser pipe coming out of the top of the seabed well have spewed an estimated 800,000 litres of crude daily into surrounding waters daily since April 22, two days after the Deepwater Horizon drilling rig exploded and sank off the coast of Louisiana.

BP said Tuesday it had spent $625 million US on response efforts to date, including grants to boost tourism in Gulf states such as Florida.