This paper considers project networks all of whose nodes have an exclusive- or entrance and whose arc weights consist of the execution probabilities and distribution functions of the durations of the respective project activities. EOR networks have some nice properties, for example, a set of Markov renewal processes can be assigned to such a network. The renewal functions of those processes correspond to special activation functions of the network and can (approximately) be computed very efficiently. At last a method for the complete evaluation of an EOR project network in the sense of time planning is presented.