NEARLY THREE YEARS AFTER A DEADLY RIG EXPLOSION IN THE GULF OF MEXICO TRIGGERED THE UNITED STATES' WORST OFFSHORE OIL SPILL, A TRIAL STARTED MONDAY TO ASSIGN BLAME AND DETERMINE HOW MUCH MORE BRITISH OIL GIANT BP AND OTHER COMPANIES INVOLVED SHOULD PAY.

BP CLAIMS IT HAS ALREADY RACKED UP MORE THAN $24 BILLION IN SPILL-RELATED EXPENSES. AND HAS ESTIMATED IT WILL HAVE TO PAY ALMOST TWICE THAT TO FULLY RESOLVE ITS LIABILITY FOR THE DISASTER.

BUT THE TRIAL ATTORNEYS FOR THE FEDERAL GOVERNMENT, GULF STATES AND PRIVATE PLAINTIFFS HOPE TO CONVINCE THE JUDGE THAT THE COMPANY IS LIABLE FOR MUCH MORE.

{Melanie Driscoll, National Audubon Society}

"We want BP to pay. We want them to be accountable for being grossly negligent. Putting their bottom line ahead of human life, bird life, our seafood, our economy, is unacceptable. It's a price the American people have paid, and we want BP to have to pay that price."

ELEVEN WORKERS DIED WHEN THE RIG EXPLODED IN APRIL 2010.

BY THE TIME BP FINALLY CAPPED THE SPEWING WELL, AN ESTIMATED 172 MILLION GALLONS OF CRUDE HAD LEAKED INTO THE GULF...FOULING MARSHES AND BEACHES, KILLING WILDLIFE AND CLOSING VAST AREAS TO FISHING.

SCIENTISTS WARN THAT THE SPILL'S FULL EFFECT ON THE GULF FOOD CHAIN MAY NOT BE KNOWN FOR YEARS.

{SOT: Steve Cochran, Environmental Defense Fund}

"Trials are about justice and this is justice that's been a long time coming. So I think that people are very excited that this is beginning today, hopeful that they'll get a result which will send a very powerful signal to every operator in the Gulf that this is too important to cut corners to try to save a buck."

LAWYERS FOR BP WILL MAKE THEIR CASES LATER MONDAY.

KELLY DASCHLE, ASSOCIATED PRESS.