Merging utilities are frequently required to share the economic benefits of a merger with ratepayers. These benefits are often measured using stock price movements at the time of the merger announcement. While event studies of this sort can be a powerful and appropriate tool, improper application and interpretation can lead to misleading conclusions. In this paper, we review the basic event study approach to merger evaluation and discuss some of the complicating factors. We describe both flawed and correctly done event studies submitted in the merger application of SBC Communications and Pacific Telesis and some additional case studies.