China National Offshore Oil Corp., China’s third-biggest oil company, may bid more than $13 billion for El Segundo-based oil and natural gas producer Unocal Corp.

CNNOC is still mulling over the bid, which was first reported in the Financial Times on Thursday.

The Wall Street Journal said that CNOOC’s interest in Unocal is still “highly preliminary” and that there are no assurances a deal will be made.

Bloomberg News, on the other hand, reported Friday that investors and analysts said $13 billion is too expensive. The news service said the price may be too high since CNOOC’s market cap is only $21 billion.

Unocal shares were up 0.7 percent to $44.45 Friday morning after they jumped 7.7 percent to $43.44 on Thursday soon after the potential bid was announced.

An acquisition of Unocal, the ninth largest oil producer in the United States, would dwarf previous purchases of U.S. companies by mainland Chinese rivals. China is hungry for energy resources as it seeks to power its fast-growing economy amid dwindling local oil output.

Unocal has oil production assets in the Gulf of Mexico, as well as Asian countries of Thailand, Indonesia, Bangladesh and Myanmar. Acquiring Unocal would more than double the Chinese company’s current production, the Financial Times reported.