Large blackouts are economically costly and socially disruptive, but in some cases can also be beneficial to investors in publicly-traded utilities. Large blackouts, particularly those that damage capital equipment, can increase future cash flows of utilities if replacement capital expenditures are permitted to be included in the rate base. The semi-strong version of stock-market efficiency suggests that these future cash flow increases will be reflected in utility stock prices following blackouts (but before the conclusion of any rate case proceedings). We use an event-study framework to examine abnormal returns for U.S. Electric utilities in the 60-day period following large blackouts. In many cases utility stock returns decline immediately following the blackout as cash reserves are depleted. In the case of blackouts that are unlikely to involve large-scale capital replacement, the blackout has little impact on abnormal returns over a longer time horizon. In the case of blackouts caused by natural disasters or extreme weather, we observe that fast recovery times (one week or shorter) are associated with a slight increase in abnormal stock returns, suggesting that investors have confidence that future rate cases will turn in the utility's favor. Finally, blackouts affecting more than one million customers and those that take more than 10 days to achieve full restoration are associated with a decline in abnormal stock returns for affected utilities, this decline persists for several weeks following restoration.