Some oil naturally would be consumed by microorganisms or degraded by sunlight and wave action, but oil might also wash ashore from Louisiana to Florida and up to the Carolinas.
Past experience in the Gulf of Mexico has been sobering. In 1979, a Mexican-owned rig called Ixtoc-1 suffered a blowout and collapsed, and 140 million gallons of oil escaped into the water. Pemex, the Mexican oil company, drilled two relief wells -- and even then oil kept escaping for three months after the first one was finished.
Engineers say major oil accidents are relatively rare, considering the amount of crude that is pumped out of the ground around the world. But the technology to bring a blown well under control has not greatly advanced since the Ixtoc accident, which remains the world's largest.
President Obama, on his third visit to Louisiana since the BP accident, said today, "It is way too early to be optimistic."