Organizations are increasingly adopting Knowledge Management Systems (KMS) to realize firm and operational level benefits. Many KMS fail to yield desired outcomes due to the lack of understanding of the antecedents of successful KMS. Prior studies have established organizational culture as a key antecedent of successful KM. This study investigates the relationship between KMS effectiveness, in terms of its impact on performance, and organizations’ knowledge culture. We develop a model of organizational knowledge processes and employ simulations to examine how the cultural values that govern the employees’ knowledge seeking and sharing propensities influence the impact of KMS on decision making performance. We find that knowledge seeking propensities have a greater influence on KMS effectiveness than knowledge sharing propensities. We also find organizational cultures that foster such knowledge sharing behaviors can expect greater and sustainable performance gains if proactive knowledge seeking is incorporated into work processes.