Representatives for Mr. Granger declined requests for comment, and he wasn't interviewed by the law firm for the report.
Mr. Trotman said that he informed other members of the country's cabinet.
The report, commissioned by Mr. Trotman, supported his position that he briefed the cabinet about his intentions to renegotiate, and cited Venezuela concerns as a key driver for the government.
Jan Mangal, who served as petroleum adviser to Mr. Granger from 2017 to 2018, believes the government got a bad deal.
"We had all of the bargaining power and it was just given away," said Mr. Mangal, a former Chevron project manager and native of Guyana.
A vocal critic of the deal, Mr. Mangal well understands it has become divisive. One of the deal's defenders in Guyana is his brother, Lars Mangal, who is a lead investor in one of Exxon's largest local service providers, Guyana Shore Base Inc.
"We have completely different views and objectives," Jan Mangal said. "It has been tough, I'm not going to pretend that has been OK in terms of the family." The brothers say that while they respect each other's views, their difference of opinion has led to some tough conversations at the dinner table.
Lars Mangal, a former executive for oil field service giant Schlumberger Ltd., said he believes his brother is missing the forest for the trees. He said Guyana could perhaps have extracted better concessions from Exxon, but getting oil flowing quickly was paramount, especially because of long-term questions about global demand for oil.
"You have to think about the macro and maximizing your potential as early as possible," Lars Mangal said. "It's good to have debate, don't get me wrong, but I certainly hope that my views prevail."
Mr. Trotman was stripped of the oil portfolio in 2018 after the government created a new energy department. He said he and the deal he signed have been unfairly villainized by some of his compatriots. He hopes oil money will soothe hard feelings.
"I'm a man of great faith and I believe it's going to be a true blessing for Guyana," he said. "I expect it will bring us closer together."
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