RIO DE JANEIRO, Oct 31 (Reuters) - Brazilian Senator Jean Paul Prates, a close ally of President-elect Luiz Inacio Lula da Silva, is a strong candidate to head state-run oil company Petrobras next year, according to three people familiar with the matter.

Lula, who defeated President Jair Bolsonaro in a runoff vote on Sunday, has still not made a decision, said the sources, who requested anonymity to comment on internal discussions.

Prates and the Lula campaign did not immediately respond to requests for comment.

Lula's incoming government is expected to take a more hands-on approach to energy policy than Bolsonaro, including a larger state role in oil refining and fuel pricing, according to comments by Lula, his advisers and their policy papers.

Shares in Petrobras closed 8.5% lower on Monday, the worst performer on the Bovespa index.

One of the sources said Lula had turned frequently to Prates for guidance on the oil and gas industry during the campaign.

But his appointment may need to overcome obstacles in the internal bylaws of Petrobras, which bar the nomination of a person who has acted in the last 36 months as part of the decision-making hierarchy of a political party.

Petrobras rules also prohibit the nomination of someone with a senior role on an electoral campaign in the last three years. (Reporting by Rafaella Barros and Marta Nogueira; Writing by Peter Frontini; Editing by Brad Haynes and Rosalba O'Brien)