In this paper we analyse the requirements of performing parallel transaction-oriented simulations within loosely coupled systems like Ad Hoc Grids. We focus especially on the space-parallel approach to parallel simulation and on synchronisation algorithms for discrete event simulation that are suitable for transaction-oriented simulation and the target environment of Ad Hoc Grids. To demonstrate our findings, a Java-based parallel simulator for the transaction-oriented language GPSS/H is implemented on the basis of the most promising Shock Resistant Time Warp synchronisation algorithm and using the Grid framework ProActive. The analysis of this parallel simulator shows that the Shock Resistant Time Warp algorithm can successfully reduce the number of rolled back Transaction moves but it also reveals circumstances in which the Shock Resistant Time Warp algorithm can be outperformed by the normal Time Warp algorithm. Possible improvements to the Shock Resistant Time Warp algorithm are s...