国际英语新闻：Obama vows "relentless" efforts to stop oil leak

Those three companies face intense political pressure in the aftermath of an explosion that sank Transocean's Deepwater Horizon rig as it was finishing a well for BP. The accident killed 11 people and oil is still flowing unchecked from the ruptured well.

Halliburton joins BP and Transocean because it provided a variety of services on the rig and was involved in cementing on the well to stabilize its walls.

Obama also said responsibility rests with the federal government, too, saying oil drilling permits had been granted without appropriate environmental reviews.

"That cannot and will not happen anymore," Obama said. He announced a new examination of environmental reviews that happen before oil and gas development goes forward.

"I'm not going to rest or be satisfied until the leak is stopped at the source, the oil in the Gulf is contained and cleaned up, and the people of the Gulf are able to go back to their lives and their livelihoods," he vowed.

The Deepwater Horizon drilling rig, owned by Transocean and leased by BP, sank April 22 some 52 km off Venice, Louisiana, after burning for roughly 36 hours. The untapped wellhead continues gushing oil into the Gulf of Mexico.