Comparison of previously compiled compressibility values obtained by various researchers [Dymond and Smith 1980, Hilsenrath et al. 1955, Span et al. 2000, Lemmon et al. 2000] shows agreement to within 10 × 10-6 in the 270 K to 330 K temperature range at 100 kPa. Perhaps more valuable is that this level of agreement is achieved between compressibility measurements made by the traditional PVT method and by the more recent speed of sound techniques [Trusler et al. 1997]. Based on this information, a relative standard uncertainty of 10 × 10-6 will be used for the experimental measurements of compressibility. This uncertainty is for a pressure of 100 kPa and it scales with density. The residuals of the equation fitting process to the experimental data are negligibly small (