(adds Bentham comment, Petrofac statement on credit facility)
LONDON, May 30 (Reuters) - Litigation funder Bentham Ventures said on Tuesday it was proposing to launch a shareholder action against British energy services company Petrofac to recover losses linked to an investigation by Britain's Serious Fraud Office.
Bentham said it was contemplating funding legal proceedings against Petrofac on behalf of investors who held shares before May 12, the date the SFO confirmed it was investigating Petrofac in connection with a probe into Monaco-based Unaoil.
The company's shares have fallen by half since then.
Bentham, which has been in touch with the top 40 Petrofac shareholders, will wait to see how the SFO case develops before launching any case, Jeremy Marshall, chief investment officer at Bentham Europe, told Reuters.
Petrofac declined to comment on the proposed shareholder action.
Petrofac shares fell after the May 12 SFO announcement, and took a second hit on May 25 when Petrofac said it had suspended its chief operating officer in response to the investigation.
Bentham said the legal proceedings would likely focus on factors such as whether Petrofac "failed to disclose material information regarding its business, its performance and prospects".
"Petrofac shares fell 30 percent to close at 389 pence on 26 May 2017 which, together with an earlier fall following the 12 May statement, has led to an aggregate fall in share price in excess of 50 percent leaving shareholders with significant losses," Bentham said in a statement.
Separately, Petrofac announced on Tuesday that $1 billion of its $1.2 billion revolving credit facility had been extended to June 2, 2021 from June 2, 2020, with the assent if its lenders.
The remaining 200 million would mature on June 2, 2020, the company said in a statement. (Reporting by Simon Jessop, Lawrence White and Sanjeeban Sarkar; editing by Jason Neely and Adrian Croft)