Analysis of the determinants of the performance of national oil companies (NOCs) is and has always been among the most discussed topics in specialized literature. In this context, the uneven path experienced by two major Latin American NOCs - Petrobras and Pemex - is striking. Our work seeks to explain the uneven performance, focusing on the productive aspects. In particular, we analyze the oil fiscal regimes in Brazil and Mexico as a very crucial aspect - though not the only one - within oil-rich countries that may shed light on the disparities between Petrobras and Pemex. The contribution of our work to the existing literature derives from the relationship that we establish between the characteristics of the respective oil fiscal regimes and the productive performance of the two NOCs, with special consideration paid to the ways in which a fiscal regime contributes, or not, to promoting and guiding the investment efforts of companies. We compare investment, production, and reserve indicators of Pemex and Petrobras and conclude that the Mexican and Brazilian oil fiscal regimes can largely explain the productive and investor performance of both NOCs.