Knowledge management has been recognized as one way for organizations to gain a competitive advantage. Despite being one major technique to facilitate knowledge management, technological knowledge management systems (KMSs) often fail because their implementation does not consider when people choose to share knowledge. The present research draws upon accountability theory, social exchange theory, and the Five Factor Model of Personality to examine how two contextual factors (i.e., evaluation and evaluation-plus-reward), perceived benefits, and personality characteristics are related to individuals' intention to share knowledge and their actual knowledge sharing via a KMS. A lab and a field study using a longitudinal quasi-experimental design were conducted to test the study hypotheses. Three experimental conditions were implemented for each study, including a control condition, an evaluation condition, and an evaluation-plus-reward condition. Surveys were used to measure study participants' personality characteristics and perceived benefits. Knowledge sharing measures included intentions and actual sharing behaviors. The findings generally provide support for the prediction that accountability mechanisms (i.e., evaluation and evaluation-plus-reward) facilitate knowledge sharing via a KMS. As expected, career-related benefits were also found to have a positive effect on both knowledge sharing intention and actual sharing. Personality characteristics interacted with the conditions. The implications of the study results for research and practice in knowledge sharing and knowledge management are discussed.