Given a connected directed graph and a spanning tree, we consider the problem of finding the set of fundamental cycles. In particular, for each cotree arc i and tree arc j, we need to know whether or not i and j are in the same fundamental cycle, and if so, whether or not arcs i and j are oriented in the same direction. This problem has application in primal network flow, longest cycle, and all-cycle algorithms. In this paper, we describe and compare three algorithms for finding fundamental cycles. Computational results are presented on a variety of directed graphs produced by a network generator. Although each of the algorithms has worst case complexity O(kp), where k and p are the number of cotree arcs and nodes, respectively, a variation of a root traceback algorithm is shown to be the fastest in almost all cases.