Mexican state-owned oil company Petroleos Mexicanos says it plans to invest $3.4 billion to build four new ultra-low-sulfur diesel plants and modernize 14 others.

The new plants will be built at three different existing refineries: Madero (northeastern state of Tamaulipas), Minatitlan (Gulf coast state of Veracruz) and Salamanca (central state of Guanajuato), Pemex said in a statement Wednesday.

Four other plants at the Salina Cruz refinery in the southern state of Oaxaca and the Tula facility in the central state of Hidalgo will undergo a thorough modernization process, the company added.

Ten other plants will undergo a less extensive renovation program.

Pemex says the diesel project, which will take an estimated 45 months and employ best industry practices, is to be coordinated by a specialized team from the company's refining unit, Pemex Refinacion, and an external oversight body. EFE