The Cove Fort-Sulphurdale geothermal resource, Utah (USA), produces from a shallow steam cap and a deeper liquid resource. In January 1999, a tracer test utilizing liquid and vapor-phase tracers was conducted to establish possible links between the injection and production wells. The quantity of tracers required for the test was estimated using the three-dimensional, multi-component, thermal reservoir simulator TETRAD. The simulations incorporated the phase behavior of the vapor-phase tracer, R-134a. Despite limited production data, well productivities, possible aquifer configurations and the total reservoir production were matched. The results showed that the predicted tracer return curves are sensitive to the positions of the discharge and recharge aquifers. The best match of the measured and predicted tracer concentrations was obtained when the recharge aquifer was placed to the east of the field and discharge occurred to the west. Published by Elsevier Science Ltd on behalf of CNR.