We propose a method to estimate mass deliverability curves for geothermal wells from a single wellhead measurement of pressure, mass flowrate and enthalpy (P, W, h)(wh) and the known reservoir pressure. This method takes advantage of dimensionless Geothermal Inflow Performance Relationships (dimensionless GIPRs), which we introduced in earlier papers. One advantage of the proposed method is that it would significantly shorten flow tests needed to obtain deliverability curves. Shorter flow tests would lessen costs and greatly reduce the volume of disposal fluids, with obvious ecological advantages; in some cases they could be the only economic option. We tested our method with data from a commercial geothermal well. The resulting estimated deliverability curves are well within the errors of the method used to measure the input wellhead parameters, which suggests that our method could be generally applicable. Further studies, already underway, are necessary to confirm this.