Faced with the challenge of reducing costs and improving competitive position, firms have recognized outsourcing as an important information systems (IS) strategic option. It has not been understood clearly what determines IS outsourcing. Based on the IS literature and transaction cost economics, cost efficiency related factors were identified, and a questionnaire survey was conducted. The results based on 181 responses from the bank executives in U.S. revealed that vendor production cost advantage and transaction risk are significant predictors of degree of outsourcing and outsourcing preference for data processing services. Insufficiency of IS funds and information technology uncertainty were found to be not only positively associated with vendor production cost advantage, but also directly associated with outsourcing preference and degree of outsourcing. Firm size is, however, not significantly related to vendor production cost advantge and IS outsourcing.