The main purpose of this study was to identify prospective chemistry teachers' mental models of vapor pressure. The study involved 85 students in the Chemistry Teacher Training Department of a state university in Turkey. Participants' mental models of vapor pressure were explored using a concept test that involved qualitative comparison tasks. Additionally, 18 participants were interviewed to explore the mental models that emerged more deeply. The researcher analyzed responses using the constant comparative method to document participants' mental models and associated reasoning patterns in sufficient detail to be of practical use to instructors. Initial analysis of the data revealed that participants have many misconceptions about vapor pressure, which are similar to those reported in the literature. A more detailed constant comparative analysis revealed that these misconceptions derived mainly from three faulty mental models of vapor pressure: (1) vapor pressure of a liquid depends on the total number of vapor particles; (2) once the liquid-vapor equilibrium is established, the number of vapor particles is fixed and does not change regardless of the external effects on the system; and (3) vapor pressure is exerted only onto the surface of the liquid. The results have practical implications for teaching vapor pressure and science in general. By eliciting the underlying mental models of vapor pressure, these findings provide valuable insights for effective instructional interventions to address misconceptions.