Reservoir storage capacity determined by the double-cycling sequent peak algorithm has been investigated in previous studies for normal and log-normal inflows. Since annual streamflows have also been found to follow the gamma distribution, it is necessary to consider this situation and to cater for other possible situations. This paper considers the distribution of the storage capacity of reservoirs with gamma inflows that are either independent or first-order autoregressive. Empirical formulae for the mean and standard deviation of the non-dimensional capacity are obtained from Monte Carlo experiments for both full and partial regulation and for the entire realistic range of the lag-one autocorrelation coefficient. It is also confirmed that the standardized capacity may be represented by a three-parameter log-normal distribution.