Two causes of poor recoverability of gas stored in aquifers are migration of gas far from the injection well and upward coning of water into withdrawal wells. Laboratory experiments and numerical simulations were conducted to study the possible use of aqueous foams to block the flow of gas or liquid to ameliorate these problems. Experiments in sandstone cores at simulated reservoir conditions showed that foam reduces the permeability to gas and liquid by typically three orders of magnitude. The rheology of foam was also investigated. It was found that steady-state pressure gradients for foam are practically independent of gas velocity but increase nearly linearly with increasing liquid velocity. This flow behavior is rationalized in terms of changes in bubble texture. A numerical simulation study showed that water coning could be significantly delayed by placing a horizontal foam lens just above the gas-water interface. Also discussed in the report are conditions for forming foam in situ, the feasibility of emplacing of foam bank, and the durability of permeability reduction. Laboratory experiments and numerical simulation indicate the potential for significantly improving the efficiency of aquifer gas storage with aqueous foams. A field trial of foam to diminish water coning is recommended. 15more » refs., 24 figs., 8 tabs.« less