Accurately identifying motives is crucial in the functional analysis of gambling behavior. In this study, a data-driven approach was followed to clarify the factor structure underlying a pool of motives for gambling, selected from the Gambling Motives Questionnaire – Financial (GMQ-F), and the Reasons for Gambling Questionnaire (RGQ), in a sample of regular problem and non-problem gamblers. Additionally, the role of gambling motives in the relationship between root behavioral activation/inhibition systems (BIS/BAS) and gambling severity, frequency, and preferences was explored using structural equation modelling (SEM). Results show that motives variance was best explained by the existence of four factors: financial motives, social motives, affect regulation, and fun/thrill. Importantly, gambling to regulate affect was directly and independently associated with gambling severity. Only the fun/thrill factor was directly related to frequency of participation in high-arousal, skill-based games, whereas all factors were related to participation in lower-arousal, chance games (with social motives negatively predicting both participation in the latter and total severity). Finally, in the SEM model, measures of BIS/BAS sensitivity were connected to gambling behavior only through gambling motives. In summary, in contrast with previous, theory-driven factorizations, there seems to be no clear-cut separation between positive and negative reinforcement-driven motives, and an affect regulation factor emerged as the only one directly associated with the risk of gambling disorder. In accordance with this dual composition, the affect regulation motives factor appears to be fueled by both BIS and BAS. Based on mesures of items’ specificity, a shortened Spanish scale (the brief Gambling Motives Inventory, bGMI) is proposed to assess gambling motives in accordance with the observed 4-factor structure.