Yesterday U.S. offshore-drilling regulators issued citations against BP and two of its contractors—Transocean Ltd. and Halliburton Co.—for violating drilling regulations that led to last year's Deepwater Horizon oil spill. The citations likely will lead to hefty fines for the companies.

The Bureau of Safety and Environmental Enforcement filed a total of 15 incidents of noncompliance against the companies. While experts expected the government to issue citations against BP, some were surprised by the regulators' citations against Transocean and Halliburton, which owned the Deepwater Horizon rig and cemented the well, respectively. According to the Wall Street Journal, contractors typically have avoided liability in similar accidents.

The government didn't specify how much BP and its contractors could face in fines, but Reuters reports they could pay up to $35,000 a day per incident.

The April 2010 spill, which was the largest spill in U.S. history, emitted more than 200 million gallons of oil into the Gulf of Mexico over a period of 87 days and killed 11 oil rig workers.