Oil giant BP has been fined a total of $373m (£182m) by the US Department of Justice for environmental crimes and committing fraud.
The fines include $50m relating to a Texas refinery explosion in 2005 that killed 15 people and injured 170 more.
That sum is the highest fine of its kind levied under the Clean Air Act.
The largest fine – $303m – relates to a price manipulation scam between April 2003 and February 2004, over which four ex-BP workers have been indicted.
“The tragic explosion at the Texas city refinery, and the pipeline leaks in Alaska, were sad reminders that our environmental laws exist both to protect the lives and safety of the public, and also to preserve our natural resources,” said Acting Attorney General Peter Keisler.
“Businesses that ignore those laws and endanger their workers and communities must be held accountable. Today’s announcement shows that they will be,” he added.
The $303m relates to price-fixing charges for manipulating the propane market in 2004. It marks a record fine imposed by the Commodity Futures Trading Commission (CFTC) for market manipulation.
“BP engaged in massive manipulation – the magnitude of this settlement reflects that the Commission will not tolerate trading abuses in our open and competitive markets,” said CFTC acting chairman Walt Lukken.
The four former BP workers accused of “conspiring to manipulate and corner” the US propane markets were named as Mark David Radley, James Warren Summers, Cody Dean Claborn and Carrie Kienenberger.
They had been employed by a subsidiary of BP America.
BP America chairman Bob Malone said “These agreements are an admission that, in these instances, our operations failed to meet our own standards and the requirements of the law. For that, we apologize”.
Mr Malone said the firm would look at ways of limiting further problems such as the “tragedy” of the Texas City disaster and the leakage of oil pipes in Prudhoe Bay, Alaska.
BP polluted a lake and land in Alaska after two oil leaks from the pipeline in March and August 2006.
The government said that BP would be monitored by an independent body for three years to ensure that it complied with the terms of Thursday’s agreement.
In opting to pay the fines, the US Government had ended the probes regarding price manipulation. In addition the firm will not face additional criminal charges for the fatal Texas accident.
However, BP could still pay further compensation under unresolved civil lawsuits.
Prior to Thursday’s announcement, BP had already spent $1.6b in compensation to victims of the Texas disaster, and has settled more than 1,600 personal injury claims.
“BP has committed serious environmental crimes in our two largest states, with terrible consequences for people and the environment,” the Environment Protection Agency said.