"An experimental method is described for testing diffusion of gases in crude oils at pressures and temperatures up to 3,000 psia and 200 F. A sampling technique was developed to withdraw by constant-pressure mercury displacement about 60 uL of oil from the diffusion cell through any of several 1/2 in vertically spaced capillary tubes and to trap about 4 ul of the oil in a specially designed microsampler. Oil trapped in the microsampler can be completely inserted in the sample inlet of a chromatograph. From analysis in a three-stage chromatograph (GL ), gas concentration in a sample is determined from the ratio of gas peak heights to area of peaks of reference components (hexanes or heptanes) in the oil. A diffusion coefficient is calculated from measured concentration profiles with known equations for diffusion in finite or semi-infinite systems, depending on whether the gas has or has not reached the end of the oil column. Results are given for a test of methane diffusing at 2,560 psia and 160 F. in crude oil from the Weber Sandstone reservoir in the Rangely field, Colorado. A constant diffusion coefficient of 3 , 34 X 10-5 cmf per sec was obtained which gives a good fit between calculated and experimental profiles determined at six times after start of diffusion. The maximum standard error of gas concentration determinations experienced with this method was ±0.88 ml per ml of gas-free oil."