Hi Sean, this time I found a bug in the step method of ParallelSequence. The step method creates n threads, which work on n chunks of the steps[] array. But the creation of the chunks only works properly if steps.length() is a multiple of n, otherwise a few elements of steps[] are never processed by the threads ! There is also another strange thing. It seems that for all simulation steps the missed elements of steps[] are always the same. But how can this be? I thought agents with the same time and the same ordering are stepped in a random order? Or does this not hold in this case because ParallelSequence is calling the agents and not schedule ?? Axel