Abstract The performance of gas-storage reservoirs subject to edge water drive is investigated through the use of digital computing techniques. The gas-water interface in the flow model is assumed to be fully segregated, and the gas-water displacement is considered to be pistonlike. Conventional approaches by the fixed boundary problems have been reported in the literatures. However, in the gas storage reservoirs, being relatively smaller in size as compared to the size of aquifer, the movement of gaswater contact is greatly affected by the amount of gas injected into or produced from the reservoir. Or in aquifer storage, the unstabilized gas-bubble grows from zero to a large value during a certain period of time. For the above moving boundary problems, the Cauchy problem of a partial differential equation has been solved numerically, because analytical solution is extremely difficult with the boundary conditions involved. A new method based on numerical techniques has been better than other conventional method, when the movement of gas-water contact is large.