SAO PAULO (Reuters) - Petroleo Brasileiro SA is selling up to three series of local unsecured bonds to raise 3 billion reais (£630 million), the Brazilian state-run oil firm said in a securities filing on Tuesday.

The debt will mature in 7 to 10 years, depending on the series, according to a preliminary prospectus related to the offering. Proceeds will be used to explore oilfields in the so-called "transfer-of-rights area".

(Reporting by Ana Mano; editing by Jason Neely)