Ultimately, a device known as a "capping stack" stopped the flow.
Transocean said that, but for BP's actions, the oil flow could have been stopped sometime in May. BP has already pleaded guilty to manslaughter and other criminal charges and has racked up more than $24 billion in spill-related expenses, including $4 billion in criminal penalties.
In the trial that began Monday, Gulf Coast states and individuals and businesses hope to convince a federal judge that the company and its partners in the drilling project are liable for much more in civil damages under the Clean Water Act and other environmental regulations. BP could be on the hook for nearly $18 billion if a judge finds that it acted with "gross negligence."
The trial resumes Monday and is expected to last for months.