A former chief engineer on a Sanford tuna-fishing boat faces up to 26 years in jail for obstruction of justice and knowingly failing to maintain an accurate oil record book, the US Department of Justice says.
James Pogue, of Idaho, was chief engineer on the San Nikunau between 2001 and 2010.
He was convicted in the US federal court last week of failing to keep accurate records of how the vessel was managing bilge waste and falsely stating that pollution prevention equipment had been used when it hadn't.
Sanford was found guilty on six of seven counts relating to the San Nikunau dumping oil from its bilges without using pollution prevention equipment and falsely claiming such equipment had been used.
The case stemmed from a Coast Guard investigation in American Samoa last year.
Each count carries a maximum penalty of $US500,000 ($NZ619,960), meaning Sanford could be liable for fines of up to $US3 million.
The company was found not guilty of one obstruction of justice charge and a forfeiture claim against Sanford for $US24 million of proceeds from the fish catch was withdrawn.
Sentencing is set down for November 16.
Another chief engineer who worked on the San Nikunau, Rolando Ong Vano of the Philippines, pleaded guilty to charges in the case and will be sentenced on September 7, according to the statement posted on the Justice Department website.
"These verdicts hold a company and one of its chief engineers accountable for polluting the waters off American Samoa with oily waste, and then trying to cover up their acts," said US Attorney Ronald Machen.
Sanford operates three large-scale freezer tuna purse seiners in the Pacific. The San Nikunau's catch was processed in Pago Pago.