President Barack Obama says he was wrong to believe oil companies were prepared to deal with a worst-case offshore spill.

At a news conference Thursday, Obama defended his call for an expansion of offshore drilling, a policy he announced not long before the disastrous spill in the Gulf of Mexico. He says domestic oil production is necessary to meet the nation's energy needs.

The president says his mistake was believing "the oil companies had their act together when it came to worst case scenarios."

"I was wrong," Obama says.

Obama says that was partly because there hadn't been a major spill recently to show that claims of fail-safe procedures needed to be re-examined.