In one experiment, the rate and pattern of responding (head entry into the food cup) under different distributions of intervals between food deliveries were examined. Separate groups of rats received fixed-time (45, 90, 180, or 360 sec), random-time (45, 90, 180, or 360 sec), or tandem fixed-time (45 or 90 sec) random-time (45 or 90 sec) schedules of reinforcement. Schedule type affected the pattern of responding as a function of time, whereas mean interval duration affected the mean rate of responding. Responses occurred in bouts with characteristics that were invariant across conditions. Packet theory, which assumes that the momentary probability of bout occurrence is negatively related to the conditional expected time remaining until the next reinforcer, accurately predicted global and local measures of responding. The success of the model advances the prediction of multiple measures of responding across different types of time-based schedules.