The purpose of this study was to develop a self-reported measure of instructor satisfaction within the context of teaching in the online environment and to validate the instrument's psychometric properties. Upon conducting an expert panel review and pilot study, the instrument was administered to 168 instructors who taught courses in the online environment at a large, public western university. Results of an exploratory factor analysis confirmed a hypothesized five-factor model: Instructor-to-Student Interaction, Affordances, Institutional Support, Student-to-Student Interaction, and Course Design/Development/Teaching. The 27-item Online Instructor Satisfaction Measure (OISM) proved to be psychometrically sound with good factor structure and high internal reliability coefficients for the instrument and its subscales.