Petrobras Scandal Shakes up Brazil Presidential Race

Those allegedly involved in the scheme were said to have received a 3 percent kickback off the oil firm's contracts with third parties between 2004 and 2012. The money swapped hands in order to maintain political support between parties, Veja said.

The names were given by Paulo Roberto Costa, former head of Petrobras' refining and supply unit, arrested in March as part of a police investigation into money laundering.

Rousseff has always stressed her credentials as a no-nonsense manager, with development of Brazil's oil riches an important part of that image.

She spoke to reporters in Sao Paulo on Saturday.

"I assure you I will take the necessary action. But I will not act based on speculation, I want the details," she said.

Expectations that the scandal would further boost opposition candidate Marina Silva are countered by the alleged involvement of Campos in the scheme.

Silva – Campos' deputy before he died in a plane crash – has spent her life campaigning against precisely the type of corruption outlined in the media reports.