State-owned Petroleos Mexicanos inked a new collective-bargaining agreement with the STPRM union that raises workers' salaries by 4.75 percent, Pemex said Wednesday.

"The accord was signed today by Pemex CEO Juan Jose Suarez Coppel and the STPRM's secretary-general, Carlos Romero Deschamps," the company said in a statement.

The new contract will enter into effect on Aug. 1 and will run through 2013.

"Suarez Coppel said this agreement confirms the company's commitment to improving its workers' conditions and raising their productivity levels to help make Pemex a more solid and competitive company and foster a new stage of growth," the statement said.

During the signing ceremony, Romero Deschamps "confirmed the workers' firm commitment to support the changes the company is pushing through as part of its modernization process and expressed his readiness to attend to workers' demands," Pemex said.

Pemex on Tuesday re-launched its Lazaro Cardenas refinery in the Gulf coast state of Veracruz after a renovation that cost 42 billion pesos ($3.62 billion).

President Felipe Calderon, who was present at the ceremony and hailed the upgraded refinery as the "most modern in Latin America," noted that a lack of investment in Mexico's oil sector for many years had resulted in outdated facilities and deteriorated operating conditions.

He said, however, that his administration has earmarked 286 billion pesos ($24.65 billion) this year to strengthen and modernize Pemex and is determined to situate the company at the vanguard of developments in the global oil industry.

Besides being the third-largest crude producer on the planet, Pemex is the government's biggest source of income and one of the world's only oil companies that controls all upstream and downstream activities, from exploration and production to refining, distribution and marketing of the final product.