U.S. prosecutors are preparing what would be the first criminal charges against BP PLC employees stemming from the 2010 Deepwater Horizon accident, which killed 11 workers and caused the worst offshore oil spill in U.S. history, said people familiar with the matter.

Prosecutors are focused on several Houston-based engineers and at least one of their supervisors at the British oil company, though the breadth of the investigation isn't known. The prosecutors assert the employees may have provided false information to regulators...