Image caption A presidential commission concluded that the explosion on the rig was caused by cost-cutting

The offshore drilling firm responsible for running the Deepwater Horizon rig has given its top executives bonuses for its "best year" for safety.

Transocean was blamed along with BP and Halliburton after last year's massive spill in the Gulf of Mexico.

Eleven workers, nine of whom worked for Transocean, died when the Deepwater Horizon exploded almost a year ago.

But Transocean said there had been a drop in the rate of recorded incidents and also in their potential severity.

'Exemplary record'

The Deepwater Horizon exploded on 20 April 2010. In the days and months that followed millions of gallons of oil poured unabated into the Gulf of Mexico, prompting President Barack Obama to call the incident America's environmental 9/11.

Before the well was capped in July, the spill fouled the coastlines of four states, scared tourists away and closed countless fishing grounds. The true environmental and economic impact may not be known for years.

A presidential commission concluded that the explosion had been caused by cost-cutting and directly blamed Transocean, BP and Halliburton for the disaster.

We recorded the best year in safety performance in our company's history Transocean annual report

Despite that, Transocean handed out huge bonuses to its executives citing the company's best year for safety ever.

The company's annual report acknowledges the explosion on the rig, but goes on to say that it exceeded internal safety targets.

"Notwithstanding the tragic loss of life in the Gulf of Mexico, we achieved an exemplary statistical safety record as measured by our total recordable incident rate and total potential severity rate," the report says.

"As measured by these standards, we recorded the best year in safety performance in our company's history, which is a reflection on our commitment to achieving an incident free environment, all the time, everywhere," it adds.

Transocean has always maintained that BP is solely responsible for the oil spill. BP contends that Transocean shares liability.