(Adds details on joint venture stakes, key dates and background on Trion field)
By David Alire Garcia and Ana Isabel Martinez
MEXICO CITY, July 27 (Reuters) - Mexico's oil regulator on Wednesday said state-owned oil company Pemex must take a minimum 45 percent stake in its first-ever proposed joint venture with would-be private partners to develop oil reserves in the Gulf of Mexico's deep waters.
Global oil majors are widely expected to bid in the December auction to help develop the Trion light oil field in the Perdido Fold Belt just south of Mexico's maritime border with the United States.
Companies such as Royal Dutch Shell and Exxon Mobil operate lucrative developments in nearby U.S. waters while Mexico has yet to achieve commercial production on its side of oil-rich Perdido due to a lack of technical expertise to tap such fields.
The call for bids to partner with cash-strapped Pemex on Trion follows the constitutional energy reform enacted in 2013 which promised to reverse a decade-long slump in crude production by luring new players to explore for and produce oil.
The regulator said the Trion joint venture will be bid out in the form of a license contract, which is similar to a concession, and will include two operators, one of which must have between a 30 to 45 percent stake in the project.
Interested bidders have until Sept. 15 to pre-qualify for the auction by meeting both financial and technical minimum requirements, while the final version of the contract and bid terms will be published on Sept. 30.
The license contract to partner with Pemex on the project will be awarded on Dec. 5. Mexico will also auction 10 separate deep water fields, including four that surround Trion, in December.
Under the terms of the energy reform, Pemex can partner with companies in exploration and production projects, but rather than being allowed to pick its partners, they will instead be selected by an auction run by the oil regulator, known as the National Hydrocarbons Commission.
The partnership will allow Pemex to share the investment needed to successfully develop the field, the company's first major deep water oil project.
The Trion field holds some 480 million barrels and will require about $11 billion worth of investment.
The field covers about 483 square miles (1,250 square km) and is located under more than 8,202 feet (2,500 meters) of water. (Additonal reporting by Adriana Barrera; Editing by Bernard Orr)