Chevron has accused U.S. lawyer Steven Donziger of bribing the judges to win the award for a group of villagers who lived in a contaminated area of northeastern Ecuador.

On the surface, the statements from Nicolas Zambrano, the former judge who testified on Tuesday, appeared to go against Chevron's claim that the judgment was a result of fraud.

But during several hours of tough questioning in a federal court in New York, a Chevron lawyer was able to zero in on several potential discrepancies in the judge's account.

Zambrano repeatedly insisted that he had authored the 188-page opinion on his own.

"It's your testimony that nobody else wrote any of those words?" asked Randy Mastro, a lawyer for Chevron, which called Zambrano as a witness.

"Yes," Zambrano replied through a translator.

In 2011, Zambrano awarded $18 billion to the villagers for contamination that occurred between 1964 and 1992 at an oil field operated by Texaco, which was later acquired by Chevron. The award was increased to $19 billion to cover fees.

Chevron has maintained that Texaco cleaned up its share of the waste before turning the field over to state-owned Petroecuador.

The oil company is asking U.S. District Judge Lewis Kaplan, who is presiding over the trial without a jury, to prohibit Donziger and the villagers from the Lago Agrio area from collecting on the judgment in any U.S. court. A victory in the United States would likely help Chevron defend against the judgment in other countries where the villagers might seek to enforce it.

Mastro worked hard in court to undermine Zambrano's credibility, quizzing him on specific sections of the judgment and asking how he could have cited French and English case law despite not speaking those languages.

Zambrano said that a woman whom he paid to take dictation also helped him in his research, pulling documents from the Internet and translating them into Spanish. He could not say whether she spoke any foreign languages.

The testimony came two weeks after another former Ecuadorean judge, Alberto Guerra, said he accepted $1,000 a month from a lawyer representing the villagers to ghostwrite Zambrano's rulings. Guerra also said Donziger was aware of the arrangement.

Testifying on Tuesday, Zambrano acknowledged that Guerra helped draft rulings for him in other cases but denied that Guerra had done so in the Chevron case. He also said he did not pay Guerra for his assistance.

When Mastro asked Zambrano why Guerra's datebook showed multiple payments of $1,000 and $2,000 from Zambrano, he said he did not know.

Earlier in the trial, Guerra testified that he would meet Zambrano on Fridays to pick up court documents and would prepare orders over the weekend before delivering them to Zambrano on Sundays.

Donziger has denied the bribery allegations.

Lawyers for Donziger have sought to discredit Guerra's testimony, saying that Chevron paid Guerra for his court appearance and gave money to his family for relocation and living expenses.

They have not yet had a chance to question Zambrano. In a statement released on Tuesday, however, the defense team said Mastro did not allow the judge to explain his answers fully.

The case is Chevron Corp v. Steven Donziger et al, U.S. District Court for the Southern District of New York, No. 11-0691.

(Reporting by Joseph Ax; Editing by Jim Marshall and Bob Burgdorfer)

By Joseph Ax