One way to reduce carbon dioxide (CO2) emissions to the atmosphere is to recover it from an energy conversion process (e.g. from stack gases) and to store it in an aquifer (a permeable, mainly sandy, underground layer). The main goal of this study was a preliminary evaluation of this kind of storage. Allowing for a large uncertainty in the geological properties, we arrived at the following tentative results. The average cost of disposal is $1.4 per ton CO2 stored. The enclosing layer of most aquifers seems impermeable enough to prevent the CO2 from rising to the surface within at least 10 000 years. The main technical uncertainty is whether the water in the reservoir can be pushed aside fast enough to prevent an intolerable pressure build-up in the reservoir. The disposal of CO2 in aquifers seems to be a feasible option in the light of existing geological knowledge. If it is a practical possibility, the opportunities are large and the costs appear to be relatively low. However, uncertainties remain in the technical sphere. These uncertainties have to be studied and dispelled before the disposal of CO2 in aquifers can be said to be called technically feasible.