Adsorption isotherms for xenon on AGOT-grade graphite, having a surface area of 0.64 meter2/ gm, were determined at −79, 0, 20, 30, and 80°C in order to determine whether the presence of helium affects the adsorption behavior of xenon. The isotherms obtained from xenon-helium mixtures were essentially the same as those obtained using pure xenon gas. The calculated heats of adsorption for xenon range between 3500 and 3700 cal/mole and approximate the heat of vaporization of 3270 cal/mole reported in the literature. The volume of xenon adsorbed (cm3 at STP) per gram of graphite, a, versus xenon partial pressure, p (mm Hg), may be expressed by the equation a = bp0.8 over the ranges of temperature and pressure investigated. The values of b are 2.14 × 10−4 and 6.33 × 10−5 at 0 and 80°C, respectively. Based on straight line extrapolations of log plots of the adsorption isosteres to higher temperatures, b would have values of 6.5 × 10−6 and 4.1 × 10−6 at 500 and 750°C, respectively. Adsorption isotherms for argon were determined at −83 and 0°C and can be expressed by the same equation indicated above. At −83° and 0°C b has values of 1.00 × 10−4 and 1.60 × 10−5, respectively.