Gas sorption and transport properties of polymers at high pressures and temperatures are important for many applications. The pressure decay method is a technique which can be used to acquire such data. A new apparatus has been developed to measure the diffusion and partition coefficients of sparingly soluble gases in polymers. Measurements can be made up to pressures of 60 bars and 200°C while measuring changes as small as 0.001 bar and holding temperature constant to 0.1°C. Data were collected for oxygen, nitrogen, and argon in poly(vinyl butyral) in the temperature range of 40 to 120°C and pressures up to 20 bar. In this study, the solubility of argon was shown to be greater than that of oxygen and nitrogen. Also, the solubility of all gases closely followed Henry's law and was temperature independent. The diffusivities of the gases were similar and can be correlated by an Arrhenius expression.