Depends on the final aftermath I'd say, i.e. on whether the politicians will need a scapegoat or not. In terms of environmental magnitude it's not yet decided

Depends on the final aftermath I'd say, i.e. on whether the politicians will need a scapegoat or not. In terms of environmental magnitude it's not yet decided whether this will make it into the Top 3 or even Top 10. According to the article around 5000 barrels of oil spill per day, with "multiple news sources" claiming it's much worse. So let's assume it's actually 50000 barrels spilling daily. Even at that rate it would still take 40 days to make it into the Top 3 of worst oil spills (according to wikipedia). However, the eventual environmental impact will most certainly not decide over whether BP heads roll or not. The financial impact on the american economy will. BP might go under even if the spill remains comparably small in the big picture - because fishies don't vote. BP might prevail even if the spill becomes the largest in history - if they pull their political strings right.