According to the New York Times, Royal Dutch Shell PLC and Brazil's Enauta Participacoes SA have registered one case each, while Petrobras has reported hundreds of cases.
The infections showcase the threat the virus poses to workers living in cramped quarters miles offshore. They have also raised questions regarding the effectiveness of extensive testing efforts on platforms.
Specifically, ANP had registered 544 active coronavirus cases, with Equinor reporting about 60 cases, largely at its Peregrino field.
In addition, Perenco has registered approximately 40 at its Pargo field, with Shell and Enauta telling Reuters they have each registered one case.
As for Petrobras, it has registered more than 300 cases among offshore workers. The company has adopted several safety measures such as large-scale testing.
Now, many oil firms are increasing universal testing and mandating long quarantine periods among workers before they go on board.
Brazil has become the country with the second-highest number of coronavirus cases after the US.