The federal lawsuit brought against Costner by Baldwin and business partner Spyridon C. Contogouris claims Costner cheated them by hiding details about the deal before they sold their stake in the company marketing the devices.

In the deal, BP agreed to make an $18 million deposit for the $52 million order for 32 oil and water separation devices. Baldwin and Contogouris claim they were duped out of part of the $18 million deposit. The 8-member jury is expected to begin deliberating on the case later this week.

Both actors once invested in Ocean Therapy Solutions, the company that acquired the rights to sell the oil-separating centrifuges. Baldwin said he was a major force in promoting the devices, which he hoped to showcase in a documentary about the April 20, 2010, Deepwater Horizon disaster in the Gulf of Mexico, the worst U.S. offshore oil spill.

BP never used the oil separators, because they sealed the blown-out Macondo well before they could be delivered.

"When you're famous it opens doors," said Baldwin, 46, known for roles in "The Usual Suspects" and "Flyboys." "My participation early on, before Mr. Costner arrived, absolutely opened doors," said Baldwin.

The testimony seems to contradict statements from Costner, 57, and the star of such movies as "Field of Dreams", "The Untouchables" and "The Bodyguard," who earlier testified that Baldwin played a minimal role in the venture.

Baldwin said he hoped to convince Costner to narrate his documentary, to be called "The Will to Drill" and feature a flight over the spill in a military helicopter with Louisiana Governor Bobby Jindal.

However, Costner seemed hesitant to enter the documentary project, Baldwin said. "I didn't get to talk with him much because he was very pensive while he was there," Baldwin said. "He seemed to be not in a good mood."

The plaintiffs want damages of $15 million to $20 million, according to Baldwin's attorney. Costner's attorney, Wayne Lee, has said that Baldwin and Contogouris are not entitled to any payments because they sold their shares in the company before the deal with BP was sealed.

(Editing by Chris Baltimore and Cynthia Osterman)

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