China Petroleum & Chemical Corp. (0386.HK), or Sinopec, and gas supplier ENN Energy Holdings Ltd. (2688.HK) said Tuesday they reserve the right to revise the terms of their US$2.15 billion offer to acquire China Gas Holdings Ltd. (0384.HK), though the market shouldn't "speculate on the possibility of any revisions."

The comment comes after Sinopec Chairman Fu Chengyu told reporters in Hong Kong on March 26 that Sinopec and ENN had offered a fair price, reflecting the fair value of China Gas.

China Gas--which controls gas pipelines serving more than 6 million customers in China--initially rejected the companies' offer, made in December, saying the HK$3.50 a share offer was "wholly unsolicited, opportunistic" and failed "to reflect its fundamental value."

Sinopec and ENN Energy said in March negotiations on the proposed deal had been extended until May 15 from their initial target date of March 31.

China Gas President Eric Leung said at the time the delay was "wholly unacceptable."

Meanwhile, China Gas said in a separate statement Tuesday it appointed ING Bank N.V. as independent financial adviser to the board committee handling the takeover bid.

-By Yvonne Lee, Dow Jones Newswires; 852-2802-7002; yvonne.lee@dowjones.com