Mexico City: Mexican authorities will hold a deep-water oil auction Wednesday, the largest since the country's government opened the sector to private industry.

So far 26 companies from 16 countries -- among them US heavyweights Exxon and Chevron, as well as the British-Dutch Shell and France's Total -- are qualified to participate in the auction of 29 oil blocks in the Gulf of Mexico, according to Mexico's oil regulator.

The auction follows a major energy reform in 2013 that saw the state-owned Pemex lose its seven-decade-old monopoly on hydrocarbon production.

With the landmark change, President Enrique Pena Nieto cleared the path for auctions in a bid to inject foreign capital into the politically-sensitive state-owned oil industry.

The fields on the auctioning block are estimated to contain some 4.2 billion barrels of oil equivalent.