The federal official leading the Gulf oil spill cleanup said Friday a new containment cap and an additional ship collecting oil could effectively contain the spill in the next three days.

Oil cleanup workers outnumber tourists at Pensacola Beach, Fla., on Wednesday. (Dave Martin/Associated Press)

The work to replace a leaky containment cap on the well's riser pipe with a tighter one will begin Saturday, said Thad Allen, national incident commander. At the same time, a ship connecting to a different part of the leak is expected to come online Sunday.

Oil will flow unimpeded into the Gulf during the cap switch for at least part of the weekend.

"I use the word 'contained,'" Allen said. "'Stop' is when we put the plug in down below."

The ultimate solution to stopping the blowout is to plug the well with cement. That can only be done when the first of two relief wells now being drilled intersects with the old well bore.

Drilling on the second relief well will stop if the first succeeds. That's expected to happen some time in mid-August.

Expected to form better seal

The new containment cap is expected to form a better seal over the well head, to allow more of the oil to be collected and sent up to ships on the surface for collection or burning.

"Technically, it's pretty achievable," Allen said. He said if the new cap can't be placed on the well, the old cap will be put back, and there are multiple backup caps available in case any one fails.

The new, tighter cap should be in place early Monday.

Allen said the ship Helix Producer, which is to be hooked to a different part of the leaking well lower than the new cap, will start collecting oil Sunday and be fully operational Tuesday.

He has previously said that the full system should be able to collect 60,000 to 80,000 barrels a day.

A shrimp boat skims oil in Barataria Bay near Venice, La., on June 6. (Sean Gardner/Reuters)

Meanwhile, Anadarko Petroleum Corp. said Friday it is not responsible for what BP says is its share of the costs of the massive Gulf of Mexico oil spill.

Houston-based Anadarko claimed it should not have to pay because it believes BP was reckless as the operator of the drilling project.

The well blew out on April 20, leading to the largest oil spill in U.S. history.

BP, as operator of the project, oversaw drilling on behalf of part owners Anadarko and Mitsui Oil Exploration Co. Anadarko owns 25 per cent of the well and Mitsui 10 per cent.

BP sent Anadarko a bill in early June for $272 million US. Anadarko spokesman John Christiansen said it has informed BP of its intention to withhold payment.

“We are disappointed they have failed to live up to their obligations,” BP spokesman Mark Salt said in a statement.

“Anadarko's refusal to pay their share will in no way affect BP's commitment to stop the leak, clean up the spill, and pay all legitimate claims as quickly as possible.”

Mitsui hasn't responded to BP's request to help pay for the spill, Salt said. The BP spokesman said Mitsui has until July 12 to pay.

So far, BP has paid more than $3 billion US to deal with the spill. According to a joint-operating agreement, Anadarko is on the hook for a quarter of the costs, so BP could be sending more bills.

With files from The Associated Press