A Burnett-isochoric apparatus was used to obtain six PVT isochores for a 79.95 mol% methane-hydrogen mixture, from 273.15 K to 5 K, and 13 to 55 bar . The Burnett method was selected since no direct measurements of mass or volume are necessary for density determinations. Densities for each isochore, obtained by intersection with a Burnett isotherm at 273.15 K , are believed to have an accuracy approaching .1% at high pressures. Pressures were measured with calibrated dead weight gages to within .1 % of the true pressure. Temperatures registered with a platinum resistance thermometer have accuracies that approach ±.1°C of the International Practical Temperature Scale of 1968. System design refinements have reduced the error contributions from elastic distortion and thermal expansion of the cells and from vertical temperature gradients. The system consists of three thick-walled spherical cells, each fabricated of the same material with equal outside to inside diameter ratios. Their centerlines lie in a single horizontal plane. Temperature gradients were .1°C or less as determined by thermopiles. As a second part of this work an empirical equation for isochoric P-T was derived and applied to a set of seventeen 5.31 mol% propane-methane isochores recently measured by Kunio Arai in this laboratory. The equation for isochores is explicit in pressure and features a linear temperature dependence augmented by terms which depend on exponentials of temperature and inverse temperature. The nonlinear terms were designed to reflect deviations from linearity and the first and second derivatives of pressure with temperature at fixed density. Among the results of a regression analysis, were the estimates of eight isochoric inflection temperatures.