(Updates with location of fields, oil sector context)
By Ana Isabel Martinez
MEXICO CITY, Aug 23 (Reuters) - Mexico's oil regulator on Tuesday approved auction terms and contracts for a dozen onshore oil and gas fields, to be bid out next year as part of a series of tenders following a landmark energy sector opening.
The second phase of the so-called Round Two tender will feature licenses, the regulator known as CNH said. Winners will be announced on April 7, 2017.
The fields are located in the gas-rich Burgos basin, in the southern state of Chiapas, as well as the Southeast basin, which is home to many of Mexico's best-producing shallow water fields. Seven of the blocs are for exploration and extraction, while five are for exploration.
Hoping to reverse slumping crude output, Mexico ended the decades-long monopoly of national oil company Pemex in 2013, paving the way for private and foreign producers to operate on their own. A sharp fall in crude prices over the past couple years, however, has made that harder.
The 2017 auctions will follow three auctions that began last year covering both shallow water and onshore blocks. The first highly-anticipated deep water auction is scheduled to take place in December. (Writing by David Alire Garcia; Editing by Simon Gardner and Alistair Bell)