Based on a mass balance and the behavior of the critical liquid volume fraction, appropriate forms of the rectilinear diameter for coexisting densities are dervied. For the refrigerants R22, R134a, and R124, a single temperature-dependent term in the rectilinear diameter was necessary to fit experimental vapor and liquid coexisting densities to determine the critical density. Internal consistency tests of coexistence density data and critical density values are developed. Critical density values for R22, R134a, and R124 are in good agreement with published values and with values calculated from published coexistence density data. Critical density values found in this study are 523.65 +/- 1.07 kg/m3 for R22, 513.02 +/- 1.98 kg/m3 for R134a, and 559.76 +/- 1.54 kg/m3 for R124.