Standard approaches to estimating the cost of capital are vulnerable to two errors when applied to sunk assets subject to economic regulation. First, investors in sunk assets usually have a valuable ability to delay commitment which is therefore an opportunity cost of investment. Second, economic regulation alters the distribution of returns to capital, and may do so in a way that eliminates pro…t potential but leaves some risk of losses. This paper studies the impact of, and the interaction between, these efects. A fundamental connection is established between the value of the real option to delay investment, the risk of losses under regulation and the rate of economic depreciation. A practical benefit of this analysis is that existing empirical methods for estimating real options can now be used to estimate the size of the 'investment incentive margin' that regulated firms should be allowed.