We assess currently available experimental data of the diameter of the coexistence curve for the gas liquid phase transition of pure fluids. Various approaches, including the direct evaluation of dielectric constant data and the analysis of calorimetric experiments, are found to support a leading vertical bar T - T-c vertical bar(2 beta) singular term in the diameter, with beta congruent to 0.326 and T-c the critical temperature. This is consistent with the predictions from "complete scaling" formulation of asymmetric fluid criticality. (C) 2016 Elsevier Ltd.