“For more than 25 years, I’ve been auditing and evaluating this situation,” Mr. Ortiz said of his beliefs about the oil quality. “I’ve turned to many agencies that had the responsibility and duty to deal with situations like this one.” He named half a dozen of them.

“No one did anything,” he said.

Mr. Ortiz is not alone in his suspicions about the fuel, which was purchased over the years from, among others, the deeply troubled Brazilian state-owned oil company Petrobras. This month another witness, a former chairman of the utility’s board, said it was “no secret” that a few large companies were rigging the prices the utility paid for oil at purported auctions.

“You don’t have to catch people with their hands in the dough to know what a cartel is,” said that witness, Luis Aníbal Aviles. The Senate hearings are scheduled to continue into March.

Similar claims are contained in a highly detailed class-action lawsuit filed by plaintiffs in Puerto Rico who say they were harmed by the dirty oil. They are invoking the federal Racketeering Influenced and Corrupt Organizations Act, or RICO.

The suit names a host of officials, oil suppliers and testing labs as defendants. It estimates that since 2002, Puerto Ricans have paid more than $1 billion too much for their electricity, because they were supporting a scheme of “undisclosed kickbacks or commissions,” run out of the Fuel Procurement Office. It seeks reimbursement plus triple damages.

While not addressing the complaint in any detail, the authority has asked the court to dismiss the lawsuit, saying the plaintiffs have not shown that a racketeering conspiracy even existed, much less harmed them. Lawyers for the many other defendants have done the same.