The English language is playing an ever-increasing role in global cultural, political, and economic domains. This underscores a rapidly growing need for good English public speaking (EPS) skills among college students and a need to better understand instructionally manipulable factors, such as self-efficacy, that may contribute to EPS skills development. Grounded in Bandura's self-efficacy theory, this study investigated the degree to which four sources of self-efficacy— enactive mastery experience (EME), vicarious experience (VE), verbal persuasion (VP), and physiological and affective states (PAS)—predicted EPS self-efficacy among 263 adult Chinese English as a foreign language learners. The overall results in the combined sample largely support Bandura's hypothesized sources of self-efficacy, with EME, VE, and VP—but not PAS—significantly making unique contributions to predicting EPS self-efficacy. The results by subsample highlight prior EPS course experience, gender, and academic major as factors that may impact the existence and the magnitude of the relationship between self-efficacy and its theoretical sources. This is particularly important for educators who wish to foster their students' EPS self-efficacy beliefs as the findings suggest that different groups of students may respond differently to their instructors' efforts. Pedagogical recommendations for EPS self-efficacy building are discussed.