A family of production decline curves for low-pressure gas reservoirs are presented for radial flow geometry with closed outer boundary and with a centrally located well. The proposed production decline curves are applicable to conventional gas reservoirs that produce gas and water simultaneously. The proposed decline curves exhibit unique characteristics for a variety of reservoir and fluid properties and pressure specifications at the well. The performance of the proposed decline curves were investigated against two different numerical simulators, and they were found to be capable of predicting the production of conventional gas reservoirs under two-phase flow conditions with good accuracy. The decline curves presented in this paper have the potential of providing a practical tool by which production performance of gas reservoirs under two-phase flow conditions can be predicted for pragmatic purposes without using sophisticated numerical models.