With the contract, Grupo Carso (GCARSOA1.MX), opens new tab becomes Pemex's partner to develop the project after its prior partner, U.S. liquefied natural gas company New Fortress Energy (NFE.O), opens new tab, pulled out last year.
Grupo Carso said in a statement that its investment as "service provider" on the Lakach project will be over $1.2 billion, while Pemex will maintain ownership of the field and its gas reserves.
In March, Reuters reported that Pemex and Slim were in talks over control and development of the project in the Gulf of Mexico.
Grupo Carso said in the statement it will build an onshore station to "treat gas and condensates for disposal at sale conditions," adding that commercial production will start in about two and a half years.
The Lakach field has been hailed as a potential gateway to a new deepwater Mexican gas frontier, and Pemex had for months made finding a new partner for the project a priority.