ASHRAE publishes thermal and transport property data for refrigerants in ASHRAE Handbook—Fundamentals every four years. However, this data is not constant, varying over the years with various releases. The main reason for this chronological variation is that revised property information, reflecting improved measurement techniques, is periodically made available in published literature.Chronologicalproperty vari-ations are investigated for four refrigerants that are represen-tative of a range of air-conditioning and refrigeration applications. R-22, R-134a, R-410a, and R-600a are evaluated at the representative possible condensation and evaporation temperatures of 40°F and 100°F (4.4°C and 37.8°C). Specifically, the vapor and liquid phases of five properties—density, specific heat, enthalpy, viscosity, and thermal conductivity, as well as surface tension—were examined. Values of these properties, starting with the 1981 edition ofASHRAEHandbook— Fundamentals are compared to 2017 reference values and also compared to values published from edition to edition. It was found that, in the extreme case, thermodynamic and transport property data can vary by nearly 30% with respect to the 2017 edition values and up to 25% between editions with a stabilizing effect appearing with modern editions.