SAO PAULO (Reuters) - Petroleo Brasileiro SA (>> Petroleo Brasileiro SA Petrobras) said Brazilian pension funds are not a party to arbitration proceedings levied against the state-controlled oil company in relation to a bribery and graft scheme that might have caused hefty losses to investors.

In a Wednesday securities filing issued in response to a newspaper article, Petrobras said the parties to the proceedings include an unnamed company and a small number of individuals. Valor Econômico newspaper said earlier in the day that claims against Petrobras could rise to 20 billion reais (4.82 billion pounds) if pension funds joined the proceedings.

The case is being handled by a special arbitration chamber at B3 SA Brasil Bolsa Balcão (>> B3 SA Brasil Bolsa Balcao) - which operates the São Paulo Stock Exchange. Listed companies and shareholders have traditionally used the B3 special chamber as a mechanism to resolve domestic commercial, legal and shareholding disputes.

Petrobras was at the centre of a kickback scheme that caused an estimated 42 billion reais in losses to shareholders and taxpayers, according to federal prosecutors. Valor said shareholders participating in the case claimed to have incurred losses between 2010 and 2015.

Common and preferred shares  (>> Petroleo Brasileiro SA Petrobras) fell 0.7 percent, respectively, on Wednesday after hitting a seven-month high in the prior session. Shares had rallied almost 4 percent on Tuesday, after a Cabinet minister raised the prospect of privatising the company in the longer term.

The process currently includes more than 200 investors and around 20 investment funds which have 5 billion reais in claims against Petrobras, Valor said. The values mentioned in the Valor report are not in the initial arbitration petition, as is required under rules set by the B3 chamber, Petrobras said.

(Reporting by José Roberto Gomes; Writing by Ana Mano; Editing by Jake Spring, Guillermo Parra-Bernal and Jonathan Oatis)