Shares in Oil Search surged as much as 19.4% on Monday after the South China Morning Post newspaper said a joint venture of China's National Petroleum Corp. was considering a bid of up to US$5 billion for the Australia oil firm.
Oil Search said it had had no formal approach from CNPC or anybody else.
The Hong Kong daily, citing unnamed sources, said CNPC Exploration, a joint venture between CNPC and Hong Kong listed Petrochina, was considering the bid.
PetroChina officials in Hong Kong were not available for comments.
The reported bid would value Oil Search's shares at about A$5.31 each, compared with its all-time high of A$4.64, based on shares on issue. The paper said some European oil companies were also looking at Oil Search.
Oil Search owns reserves in Papua New Guinea, Yemen, Egypt and Libya. Its annual report shows that it has proven and probable oil reserves of 1.43 billion barrels at the end of last year.