A partially preemptive quality of service ("QoS") scheduling model for application in an optical burst switched ("OBS") network node is described. In one aspect, the invention comprises a method for dropping only an portion of a data burst under consideration that overlaps with a portion of an already-scheduled data burst. In another aspect, the invention comprises preempting only that portion of an already-scheduled data burst that overlaps with a portion of a data burst under consideration and scheduling the data burst under consideration in its entirety. In one embodiment, the decision whether to drop a portion of the data burst under consideration or preempt a portion of the already-scheduled data burst is based on the relative priorities of the bursts. Similarly, the decision whether to perform a partial or full drop or preempt is based on the amount of overlap between the bursts.