This paper discusses the results of recent instrumental neutron-activation analysis (INNA) work identifying the obsidian sources relied upon in the Tuxtla Mountains of southern Veracruz in pre-Hispanic times. Our research indicates that Guadalupe Victoria and, secondarily, Zaragoza obsidian were the main sources imported to the Tuxtlas during the Early and Middle Formative periods. In contrast, Zaragoza became the dominant source relied upon from Late Formative times onward. Data on obsidian color and raw-material quality make it possible to extend the INAA results to the entire obsidian assemblage from the Tuxtlas.