Abstract
A probabilistic calculus, derived from Milner's SCCS, WSCCS is presented. We define a notion of bisimulation for probabilistic processes and show that it is a congruence. A simple equational characterisation is shown to be both sound and complete for finite processes. We present many examples including some extended ones. The larger examples show both the expressive power of WSCCS and the availability of simple proof methods for some complex systems.