Geothermal resources have the potential to fulfill a significant portion of the low-temperature (30–100 °C) thermal energy demand in the United States. Investment risk at the exploration stage is a primary factor limiting the development of geothermal energy projects, due to the high cost of drilling and limited reservoir data. An approach to reduce this risk is to target proven, well-characterized conventional oil and gas reservoirs. We examined the suitability of the Trenton–Black River gas fields of southern New York as geothermal reservoirs. These highly productive hydrothermal dolomite fields occur within long, narrow normal-fault–bounded, en echelon grabens that are scattered with saddle dolomite-lined vugs, fractures, and breccia. The Quackenbush Hill field was analyzed using existing data sets with geothermal purposes in mind. Key geothermal reservoir characteristics examined here include rock temperature, porosity and permeability, stimulation potential, and the risk of inducing seismicity. Results indicate that the Quackenbush Hill field would produce temperatures of ∼91 °C from a dolomite reservoir with sufficient average horizontal permeability, low vertical permeability, and significant vertical and horizontal anisotropy. In the case that adequate flow rates cannot be achieved in practice, stimulation is a feasible option from the perspective of well-field design for optimal heat sweep; however, higher-resolution data are necessary to constrain the risk of inducing seismicity. We demonstrate the technical feasibility of transitioning conventional gas fields into geothermal heat-producing reservoirs, setting the stage for future consideration of the economics of a petroleum-to-geothermal transition.