When Mexico’s energy overhaul was signed into law in August, Emilio Lozoya, the chief executive of Petróleos Mexicanos, set a goal for the state oil giant that until recently would have seemed unrealistic: to regain its position as Latin America’s biggest company. For Pemex, as the company is known, that means leapfrogging Brazilian oil majorPetróleo Brasileiro SA, or Petrobras, which holds the top spot in sales and has expansion plans of its own. Petrobras has been the star of the region’s oil sector for over a decade due to its technical expertise, growing oil production and international portfolio. Pemex’s crude production, meanwhile, has fallen for 10 years straight as the company’s shallow-water fields declined and much of its investment budget went toward squeezing more oil from older fields.