A BP employee has lost a laptop containing personal data belonging to thousands of Louisiana residents who filed claims for compensation after the Gulf oil spill.

The firm said it had sent letters to roughly 13,000 people whose data was stored on the computer, notifying them about the potential security breach and offering to pay for their credit to be monitored.

The laptop was password-protected, but the information was not encrypted.

The data included a spreadsheet of claimants' names, social security numbers, phone numbers and addresses. Curtis Thomas, a BP spokesman, said the company did not have any evidence that claimants' personal information had been misused.

"We're committed to the people of the Gulf coast states affected by the Deepwater Horizon accident and spill, and we deeply regret that this occurred," he said.

The data belonged to individuals who filed claims with BP before the Gulf Coast Claims Facility took over the processing of claims in August. BP paid roughly $400m (£250m) in claims before the switch. As of Tuesday, the GCCF had paid roughly $3.6bn to 172,539 claimants.

BP said no one would have to resubmit a claim because of the lost data.

The employee lost the laptop on 1 March during "routine business travel". "If it was stolen, we think it was a crime of opportunity, but it was initially lost," Thomas said.

BP is offering to pay for claimants to have their credit monitored by Equifax, an Atlanta-based credit bureau. Asked why nearly a month elapsed before BP notified residents about the missing laptop, Thomas said: "We were doing our due diligence and investigating."