By Jeffrey T. Lewis

SAO PAULO--Brazil's Federal Police carried out five search-and-seizure warrants Tuesday morning as part of an investigation into graft regarding the sale of oil and derivatives by state-controlled oil company Petroleo Brasileiro SA, or Petrobras.

Almost 40 police agents were involved in the searches in the city of Rio de Janeiro, where the oil company is based, and in the nearby city of Niteroi, also in Rio de Janeiro state. The police didn't provide details on what type of material was seized.

The warrants were based on information provided as part of plea deals by a Petrobras employee who faced criminal charges after a 2018 probe of corruption at the state-controlled company and by an executive of a trading company that worked with Petrobras, police said.

With their assistance, police identified at least six current or former Petrobras employees involved in a scheme to defraud the company, police said. One of the employees, who still worked at Petrobras as of Tuesday, generated unnecessary trades between the company and foreign trading companies, police said. The trading companies would then pass some of the commissions they earned on the trades back to the Petrobras employees, police said.

The police didn't provide the names of any of the people involved or of any of the other companies involved.

Some of the former employees are also being investigated for the sale of privileged information and for favoring certain foreign companies for contracts for the supply of fuel oil, aviation fuel and other petroleum derivatives, according to the police.

The searches Tuesday were part of the ongoing Operation Car Wash investigation into corruption centered on Petrobras, which also involved many other giant Brazilian companies such as now-bankrupt builder Odebrecht SA and beef producer JBS SA.

The probe also reached high into Brazil's government, with former President Luiz Inacio Lula da Silva convicted of money-laundering and corruption and jailed for almost 20 months for participating in the scheme.

Write to Jeffrey T. Lewis at jeffrey.lewis@wsj.com

Corrections and Amplifications

This headline was corrected at 3:33 p.m. ET because the headline "Brazil Police Search Petrobras Offices in Probe of Trading Graft" is incorrect. No Petrobras offices were searched. The correct headline should be "Brazil Police Execute Search Warrants in Probe of Trading Graft at Petrobras."

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10-20-20 1027ET