EXXON Mobil Corp. is in talks with PetroChina Co. to jointly explore and develop an unconventional gas block in the resource-rich Ordos basin in northern China. BEIJING Exxon Mobil Corp. is in talks with PetroChina Co. to jointly explore and develop an unconventional gas block in the resource-rich Ordos basin in northern China, according to a person familiar with the matter. A successful conclusion to the talks would mark the entry of another global energy major into a huge but undeveloped sector that China hasn't been able to develop because of a lack of technology.