Shares of BP dropped 12 percent in the opening moments of trading in London Thursday before recovering. (BP shares rebounded on Wall Street Thursday.) Traders are nervous President Obama will hit the company with massive penalties for its role in the oil spill blackening the waters of the Gulf coast. BP’s stock price has been cut in half since the Deepwater Horizon rig exploded more than seven weeks ago—it opened at its lowest price since 1997—and British Prime Minister David Cameron is set to discuss the company with Obama this week. Interior Secretary Ken Salazar has said BP should compensate other oil companies who’ve had to lay off workers during the moratorium on deepwater drilling, and the Justice Department wants to prevent BP from sending out its next dividend payment. The drop in value is bad news for U.K. pensions because they’re heavily invested in the oil giant.