Could Exxon buy BP?

Updated at 4:15 p.m. ET

Have you been noticing that everybody's favorite oil stock, BP (BP),  is, well, rising?

It has been for the last two days, and the cause is takeover speculation. Not real takeover speculation, as in there's real evidence that investment bankers and lawyers are scurrying around drawing up offer sheets and the like.

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But rather speculation from one analyst, Fred Lucas of JP Morgan Cazenove in London. Lucas thinks BP could be a takeover candidate and the only company with the money and chutzpah to take on the troubled oil giant is Exxon Mobil (XOM).

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So,  BP's shares (technically American depositary units) gained 4.4% today to $28.88. The shares are up about 5.5% from Friday's close of $27.02. In London today, the shares hit as high as 330.85 pence before finishing at 318.52 pence -- a gain of 5.2%.

(One American depositary unit represents six BP shares.)

Exxon isn't the only company that might want to bid for BP. Royal Dutch Shell's (RDS.A) name is bandied about. So are Russia's Gazprom (OGZPY) and China's PetroChina (PTR).

Lucas likes Exxon as the winner. His theory is that Exxon would like to get its hands on BP's natural-gas and oil assets and its exploration expertise.

And Exxon does have a strong balance sheet and would easily be able to access the capital markets for the cash for a potential deal.

Plus Exxon knows how to do big deals. After all, it did acquire Mobil, one of the companies spun out of the 1911 Standard Oil antitrust case.

Yes, there are antitrust concerns. Exxon would probably have to unload BP's network of service stations, Lucas wrote clients.

And he doesn't think BP will spend more than $33 billion on the spill cleanup.

And the fact is BP is now relatively dirt cheap. The oil giant  has lost more than half its value since the Deepwater Horizon rig exploded and later sank in the Gulf of Mexico. The explosion killed 11 workers and set off the worst oil spill in U.S. history.

So, Lucas figures Exxon could offer, say, 473 pence, or $42.50 (U.S.) per share -- a total value of some $133 billion. It would be roughly a 50% premium over today's price. And a bargain, considering that BP had a market capitalization of $189.3 billion before the rig explosion.

Could that happen? Maybe. Earlier this month, BP hired investment bankers Goldman Sachs (GS), Blackstone Group (BX) and Credit Suisse (CS) to help in what are admittedly difficult times.

To help fend off unwanted takeover bids? Maybe a bankruptcy? The company wasn't saying.