• ExxonMobil discussed politics of BP takeover with the White House • BP's value had once dropped by more than $100bn, since 20 April

BP said today that it was a fortnight away from finally sealing the rogue well in the Gulf of Mexico – potentially triggering bids from rivals for a company whose market value has been dramatically eroded since the April blowout.

BP, which also announced that the clean-up bill has hit $8bn (£5bn), has been viewed as vulnerable to takeover since the Deepwater Horizon accident on 20 April.

But City experts said the leaking well needed to be finally capped – putting a lid on liabilities – before anyone would dare make a move. There have been successive reports that the cash-rich US firm ExxonMobil – the biggest non-government owned oil company in the world – has discussed the political implications of a BP takeover with the White House .

While Barack Obama is said to have raised no competition objections – although some assets would probably have to be sold – industry experts believe he must be concerned about job losses at a time of high US unemployment.

Any takeover offer would fit into a wave of merger and acquisition activity across other sectors of business and would inevitably lead to redundancies.

No new oil has flowed from BP's Macondo well in the Gulf since 15 July when a cap was inserted but BP said it hoped to seal it for good in mid-September.

The bill has steadily risen since the explosion, which triggered an environmental disaster in the region and the country's worst-ever oil spill. In the aftermath, the oil company was forced to abandon hopes of drilling in the Arctic due to its tarnished reputation while BP's chief executive, Tony Hayward, bowed to pressure to resign from the end of this month.

Since the processing of claims by people affected by the disaster was transferred to the Gulf Coast Claims Facility, led by Ken Feinberg under a deal with the White House, BP has paid out some $38.5m to 4,900 claimants. Before the transfer, it had made 127,000 payments, worth about $400m. Meanwhile, more than 28,000 people, more than 4,050 ships and dozens of aircraft are still involved in the country's biggest offshore clean-up operation.

BP's future was effectively put up for formal discussion in June when the normally-conservative investment bank, JP Morgan Cazenove put out a provocative research note on BP.

Fred Lucas, JP Morgan's London-based oil analyst, looked at whether Exxon was the right player to make an £88bn bid. The US group is the financially strongest oil company, he said, adding that it could make a cash and stock offer while spinning off $50bn (£33bn) of refining and marketing assets, resulting in a bid estimated at 473p a share.

Certainly BP is very cheap by historic standards. More than $100bn was wiped off BP's market value at one stage since the 20 April explosion.

The company has instructed Goldman Sachs and Blackstone to defend against any hostile takeover bids.

One City fund manager said last night that he expected Exxon, Chevron or possibly even a Chinese national oil corporation to make a move on BP but Fadel Gheit, veteran oil analyst with the Oppenheimer brokerage in New York, said he doubted the White House would endorse a takeover that would cost more US jobs.

"When Exxon took over Mobil (in 1998) 50,000 jobs were shed within three years. The real way these mergers are made to work is by cutting costs often by massive layoffs. What politician would support that when unemployment levels are already at their highest for 40 years? It makes a lot of sense on paper but the political realities make it unlikely."

Other analysts said a move by a Chinese company was unlikely be agreed in the US, where many of BP's assets are based. Washington vetoed the takeover of Unocal by the China National Offshore Oil Corporation in 2005.