For the past couple of years, it appeared that BP (NYSE: BP) had gotten closer to star status in the Big Oil show.

As The Wall Street Journal noted on Wednesday, when the now-controversial Tony Hayward suddenly became CEO in May 2007, he maintained that he would focus "like a laser" on safety, referring to a host of blemishes that preceded his tenure. They included the company's 2005 Texas refinery explosion, which killed 15; a leaking Alaskan oil pipeline, which continues to have problems; and a general company attitude in which cost controls trumped safety.

In fairness, Hayward's regime has not been without successes. The company -- along with ConocoPhillips (NYSE: COP) and Brazil's Petrobras (NYSE: PBR) -- found the giant Tiber well in the Gulf of Mexico. And it also notched numerous deepwater discoveries offshore from Angola. In March, it agreed to pay $7 billion for a package of Devon's (NYSE: DVN) assets in the deepwater Gulf, Brazil, and Azerbaijan.

Then came April 20 of this year. Needless to say, despite numerous attempts to kill it, the company's blown-out well continues to gush oil, destroying the Gulf's environment and possibly its economy as well. The tab for BP from this horror already includes a $100 billion plunge in its market value, along with untold tens of billions in clean-up costs, fines, and compensation charges.

The final bill will be a doozy. It's clear that BP will be forced to sell assets to stay out of hock. Indeed, the entire company might go on the block, a possibility that has popped up periodically since the spill began. It's now being brought up again, and you won't be surprised to know that potential post-spill buyers may include ExxonMobil (NYSE: XOM), Shell (NYSE: RDS-A), and possibly PetroChina (NYSE: PTR).

Given the time until the relief wells now being drilled are expected to help halt the destructive gushing, a takeover seems more likely by the day. And with 40% of BP's reserves in the Gulf, a prohibition against its working in the U.S. -- not an unrealistic possibility -- could deeply slash the buyout price the company might command.

Nevertheless, I'd wager that a takeover would most likely involve Exxon. The biggest of Big Oil has the ideal balance sheet, along with a solid management team with experience integrating a sizable acquisition. So let's stay tuned to these changing events. In the meantime, a few shares of ExxonMobil wouldn't hurt your portfolio.