According to Brazilian website Grande Prêmio, Petrobras has signed a deal with McLaren to supply fuel from 2019 onwards.
The fuel will be jointly developed during 2018 by McLaren and Petrobras. This deal doesn't include the hiring of any brazilian driver. It will be officially announced tomorrow.
Also interesting to note that the brazilian driver Sergio Sette-Câmara is driving alongside McLaren's reserve driver Lando Norris in this year's F2 season. Sergio has been sponsored by Petrobras in the past.