Interactive simulation systems supporting the post-simulation analysis, presentation and interpretation of results have been developed and will continue to evolve. Post- simulation definition and computation of performance measures should be one important capability of such systems. We propose a method for accomplishing this objective. A simulation language neutral form of a discrete event trace contains the information from which the performance measures are computed. Computational procedures for typical performance measures: transaction time delays, numbers of transactions concurrently engaged in an activity or in a queue, time intervals between occurrences of the same event, and the state distribution of resource units are given. A software library for managing traces and performing the needed computations is described. An example shows an illustrative application of the method to three simulation languages: SLAM II, GPSS, and INSIGHT.