This study examined the impact of two epistemic commitments on the quality of college students‟ scientific reasoning in the domain of hydrostatics. These were the commitment to the consistency of theory with prior knowledge and commitment to the consistency of theory with evidence. Participants were 12 sophomore science majors enrolled in a large Midwestern university in the United States. They were first administered a 10 short-answer item questionnaire to assess their understandings of buoyancy, and then participated in an individual, think-aloud interview centered on four paper-and-pencil scenarios involving systems of objects immersed in water. During the interview, participants also were asked to justify their responses and explain certain reported “observations” in each scenario. The interviews aimed to explore the impact of participants‟ epistemic commitments on their reasoning. A majority of participants did not demonstrate coherent reasoning schemes when working with buoyancy problems. To be sure, participants‟ prior conceptions of buoyancy interacted with the target epistemic commitments in impacting their reasoning. Still, there was a discernable impact for the target epistemic commitments on the quality of participants‟ reasoning.