Diffusion of short chain n-alkanes was found to be faster in the polydimethylsilicone elastomer SE-30 than in the polydimethylsilicone oil SF-96-2000. The opposite was true for the longer chain n-alkanes suggesting that choice of stationary phase would depend on the chain length of sample components. The dependence of diffusion on chain length is explained as being the result of competition between the effects of free volume and viscosity for dominance in the diffusion process. Peak skewing was not found to be a problem in SE-30 down to 50°C contrary to previous findings. The equation In K = -1.805–0.570 C + (950 + 905 C)/1.987 T, where C is the carbon number of the n-alkane, was found to be excellent for determining partition coefficients of n-alkanes in SE-30. The entropy and enthalpy for evaporation of n-alkanes from SE-30 were determined to be: ΔS = 1.987(1.805 + 0.590 C) cal/deg - mole and ΔH = 950 + C cal/mole.