The American administration said Monday it will allow 13 companies to resume deepwater drilling without any additional environmental studies, just months after saying it would require strict reviews for new drilling after the British Petroleum oil spill in the Gulf of Mexico.

The government said it was not breaking its promise to require environmental reviews because the 13 companies already started drilling the wells without detailed environmental studies.

Drilling was suspended last year when the administration imposed a months-long moratorium following the British Petroleum spill in April last year. The ban was lifted in October, but drilling has not yet resumed in waters deeper than 500 feet (152 meters) in the Gulf of Mexico.

U.S. officials said the 13 companies must comply with new policies and rules before resuming activity at 16 wells in the Gulf of Mexico. All but three are exploratory wells, and the idea is to determine whether and how much oil there is in that place.

The administration has been under heavy pressure from the oil industry, Gulf state leaders and congressional Republicans to speed up drilling in the Gulf of Mexico.

A federal report said the moratorium probably caused a temporary loss of between 8,000 and 12,000 jobs in the Gulf region.

The 13 companies that received the notice are: ATP Oil & Gas Corp.; BHP Billiton Petroleum (GOM) Inc.; Chevron USA Inc.; Cobalt International Energy; ENI U.S. Operating Co. Inc.; Hess Corp.; Kerr-McGee Oil & Gas Corp.; Marathon Oil Co.; Murphy Exploration & Production Co.-USA; Noble Energy Inc.; Shell Offshore Inc.; Statoil USA E & P Inc.; and Walter Oil & Gas Corp.