Operating room (OR) scheduling is one of the most important tasks for hospital managers in terms of improving efficiency in hospitals. In this study, scheduling policies for elective and emergency procedures that minimize the total expected cost of OR operations are investigated. A simulation optimization approach is used to develop schedules and evaluate the operational impact of reserving capacity for emergency patients in an OR system. In order to mitigate the possible negative effects of unused capacity should a lower than expected number of emergency cases arrive, assigning any unused capacity to standby patients is examined. This study looks at the effect of hospital size in terms of the number of surgeries performed, mean surgery duration, and the variability in surgery duration on scheduling policy based on empirical data from three hospitals. Specifically, we investigate the best policies in terms of OR efficiency with and without reserved capacity for emergency arrivals and different probabilities for standby patient availability.