LONDON—Tony Hayward thought he had finally slain all of BP PLC's demons. Now a new one has reared up, and it's the size of Puerto Rico.

BP's chief executive is coming under mounting pressure over the vast spill spreading in the Gulf of Mexico, which was caused when a giant drilling rig there caught fire and sank, with the loss of 11 crew members. The oil, still spewing from the well on the ocean floor, threatens to blacken the Louisana shoreline, and BP's reputation.

From...