Reza Zarrab, the government’s star witness in a trial involving a billion-dollar conspiracy to smuggle gold for oil in violation of United States sanctions on Iran, testified on Tuesday that he had made huge sums of money in the scheme — but he could not recall the precise amount.

“I don’t remember exactly but it could be $100 million,” Mr. Zarrab, who helped orchestrate the scheme, told the jury through an interpreter. “Maybe more than that. Maybe $150 million.”

Mr. Zarrab’s testimony came on his fifth day on the witness stand in Federal District Court in Manhattan as he was cross-examined by a lawyer for a Turkish banker, Mehmet Hakan Atilla, who is on trial for his alleged involvement in the sanctions evasion.

Mr. Zarrab, a wealthy Turkish-Iranian citizen who was arrested on a 2016 family trip to Disney World, testified last week that in 2012, Recep Tayyip Erdogan, then Turkey’s prime minister and now its president, personally ordered that two Turkish banks be allowed to participate in the scheme.