Abstract: While constraining the speculation in Time Warp (TW) tends to de crease the number of false event executions, it also introduces an opportunity cost when the processors are not fully utilized. To obtain good run-time performance such a trade-off must be optimized. This paper studies the implications of regulating speculation in TW, and develops an analytic framework for optimizing the elapsed time of TW simulators. By aggregating the effect of three time components, namely computation time, communication time and processor idle time, our analytic framework optimizes the degree of speculation for better performance. Our experiments on a Fujitsu AP3000 distributed-memory parallel computer simulating several applications show that the predicted performance metrics deviate from the measured values by less than 8%. Both the analytical and experimental results have ascertained that speculation without rollbacks may not produce the best elapsed time. Instead, a controlled degree of causality error is preferred in most practical cases.