A novel technique called reverse circuit execution is presented as an efficient approach towards integrated parallel execution of multiple sequential circuit simulators. The unique aspect of this approach is that it does not require source code modifications to either simulation engines or circuit models, and hence holds appeal in situations where parallelism is desirable but without access to simulator and/or model source code (as in the case of commercial simulators with proprietary code concerns). First, algorithms and methodology are presented for transforming an input circuit into another equivalent circuit that is capable of both forward and reverse execution. Following that, it is shown how the transformed circuit can be used towards optimistic synchronization of multiple circuit simulators. As an end result of using our approach, it will be possible to efficiently co-simulate logic circuits partitioned across multiple commercial simulators, by synchronizing their execution using optimistic concurrency protocols.