Integrating self-determination theory and the theory of planned behavior in studying biogasoline purchasing behavior in Vietnam

Rapid socio-economic development has intensified environmental degradation and increased reliance on fossil fuels, raising concerns about the sustainability of current energy consumption patterns. In response, Vietnam has promoted renewable energy alternatives such as biogasoline; however, consumer adoption remains relatively limited. This situation highlights the need to better understand the behavioral mechanisms underlying biogasoline purchasing decisions. This study investigates the determinants of biogasoline purchasing behavior in Vietnam by integrating the Theory of Planned Behavior (TPB) and Self-Determination Theory (SDT). The proposed framework examines how consumers’ attitudes, green intrinsic motivation, and green extrinsic motivation influence biogasoline purchase behavior, both directly and indirectly through purchase intention. Data were collected from 313 consumers across Northern, Central, and Southern Vietnam via an online survey, and the research model was tested using Partial Least Squares Structural Equation Modeling (PLS-SEM). The results show that consumers’ attitudes toward biogasoline significantly influence both purchase intention and actual purchasing behavior. Green extrinsic motivation emerges as the strongest predictor of purchase intention and also exerts a direct, though weaker, effect on purchase behavior. In contrast, green intrinsic motivation does not significantly affect purchase intention but directly promotes actual purchasing behavior, suggesting that intrinsically motivated consumers may act without explicit prior planning. Purchase intention is also confirmed to play a partial mediating role between psychological factors and purchasing behavior. These findings contribute to the literature on green consumption and behavioral economics by clarifying the distinct roles of intrinsic and extrinsic motivations in renewable energy consumption within a developing economy. The study also offers practical implications for policymakers and energy providers in designing targeted incentives and communication strategies to encourage biogasoline adoption and support Vietnam’s sustainable energy transition.