A top construction company executive has told investigators he paid $36.1 million in bribes to executives at state oil giant Petrobras, which is being rocked by Brazil's biggest ever corruption scandal, local media reported.

Eduardo Leite, vice president at the construction firm Camargo Correa, told prosecutors the bribes stretched from 2007-2012. He is cooperating with authorities in exchange for a potential future reduction of his sentence, G1 news portal reported.

The construction firm is allegedly one of those that paid executives at Petrobras to give them contracts in exchange for overcharging. Then the executives would skim the difference.

"It was very easy," Leite was quoted as saying in the report. He said overcharging on government contracts sometimes reached as high as 20 percent.

Brazil's President Dilma Rousseff chaired the Petrobras board during much of the period when the alleged corruption took place, though she has not been implicated in the scandal.

The scandal has taken a heavy toll on Petrobras, the largest company in the world's seventh-largest economy.

Its chief executive and board of directors resigned in February, after the company lost nearly $9 billion in stock value after being downgraded by two ratings agencies.