MEXICO CITY, July 6 (Reuters) - Four companies have bowed out of the initial installment of Mexico's so-called Round One oil auction, the first step in the country's historic sector opening, regulator CNH said on Monday.
The Mexican units of Noble Energy and Glencore , as well as Colombian national oil company Ecopetrol , have all asked to exit the competition for 14 shallow water oil fields set to be awarded on July 15.
Thailand's PTT Exploration and Production Public Company Limited also dropped out.
The CNH did not specify why the firms decided they would no longer participate in the initial auction for shallow water exploration blocks located along the southern rim of the Gulf of Mexico.
Some oil companies have pointed to tough rescission clauses built into the auction's production-sharing contracts as a potential problem.
Meanwhile, Premier Oil opted to desist from seeking potential opportunities as an individual operator, but will instead join an existing consortium prequalified for the auction.
The July tender now features 18 companies prequalified as individual operators, while the slimmed-down prequalified consortia stand at seven.
Reporting by David Alire Garcia; Editing by Andrew Hay