The federal lawsuit lodged against Costner by Baldwin and business partner Spyridon C. Contogouris alleges that Costner, best known for his performance in "Field of Dreams" and "The Bodyguard," cheated Baldwin and Contogouris out of their share of a multimillion-dollar deal under which BP bought 32 oil and water separation devices developed by a Costner-owned company.

Day two of the case focused on emails and text messages among the parties before BP made an $18 million advance payment for oil extraction devices to be used to clean up after the April 20, 2010, Deepwater Horizon disaster, the worst offshore oil spill in U.S. history.

Both actors once invested in Ocean Therapy Solutions, the company that owned the oil-separating centrifuges. Baldwin and Contogouris claim that Costner and his associates defrauded them by hiding details of their deal with BP. The plaintiffs seek damages of $15 million to $20 million, said James Cobb, attorney for the plaintiffs.

Plaintiffs will prove that Costner and his associates lied repeatedly to exclude them, Cobb told Reuters. "Lies are like potato chips - no one can tell just one," Cobb said.

Costner's defense contends that the plaintiffs were not actual investors in Ocean Therapy Solutions at the time of the BP deal, and therefore their claim is not valid.

Both actors were expected to appear in court every day of the trial before U.S. District Judge Martin L.C. Feldman and eight jurors.

Neither has testified yet and the two have avoided any direct contact. Costner and Baldwin avoided direct eye contact in the courtroom but their body language sometimes reflected the tension between the parties.

Baldwin, 46, in brown plaid blazer, gray shirt and pants, occasionally turned toward his lawyers and rolled his eyes or shook his head during Smith's testimony. The youngest of four brothers all of whom are actors, he is known for his roles in "Threesome," "The Usual Suspects" and "Flyboys."

Dressed in a gray blazer, light blue shirt and dark pants, Costner, 57, declined to comment on the lawsuit, but remarked upon returning to the courtroom from a lunch break: "It's too beautiful a day to be in court."

(Reporting By Chris Baltimore; Editing by Eric Walsh)

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