China may merge its state-owned oil companies to create giants that will be more efficient and capable of taking on overseas rivals like Exxon Mobil Corp., the Wall Street Journal reported.

The country’s leaders have asked government economic advisers to study the possible mergers, the Journal said, citing unidentified officials familiar with the research. One plan would combine the country’s largest oil companies, China National Petroleum Corp., or CNPC, and China Petrochemical Corp., or Sinopec, according to the newspaper. Other options include merging China National Offshore Oil Corp., or Cnooc, with Sinochem Group.

No timetable is set for a decision on whether or when to proceed with the mergers, according to WSJ.

China is consolidating other industries, combining the country’s two biggest trainmakers to boost exports of high-speed rail technology. CSR Corp. will acquire smaller competitor China CNR Corp. by issuing 1.1 new shares to CNR investors for each share they own, the two companies said in a joint statement in December.

Qu Guangxue, a Beijing-based spokesman for CNPC, didn’t respond to calls to his office seeking comment outside of business hours in China. Sinopec and Sinochem spokesmen in Beijing also couldn’t be reached. A Beijing-based spokeswoman for Cnooc said the company won’t comment on market rumors.

Concerned over slowing growth, China has pledged to give markets a decisive role in its economy.