The London-listed company said in a statement that talks with both Apollo Global Management and Bain Capital were ongoing and that the competing suitors now had until Nov. 5 to make firm offers or walk away from RPC.

Under British rules, the pair had faced a deadline of 5 p.m. London time (1600 GMT) on Monday to declare their intentions towards RPC, which has a market value of about 3.2 billion pounds.

In a separate statement, RPC said it had generated first-half revenues from continuing operations of 1.9 billion pounds, which was ahead of the same period a year earlier and included organic growth of about 3 percent.

"The group's margins and operating profitability levels generated by continuing operations (before and after adjusting items) remain in line with management expectations," RPC said, adding that polymer price changes had caused a "headwind" during the period.

RPC has grown with the help of a spate of acquisitions in recent years, which have complicated its accounts and prompted Northern Trust Capital Markets analyst Paul Moran to raise concerns about the company's cash generation.

The stock has become a target for short sellers, with funds including Marshall Wace and GLG Partners betting on a fall in RPC's share price, according to date compiled by Britain's Financial Conduct Authority. RPC shares closed down 4.2 percent at 779.6 pence.

(Reporting by Ben Martin; Editing by Adrian Croft)

By Ben Martin