Adsorption and diffusion of normal alkanes and alkenes having carbon numbers from C8 to C15 have been measured in the liquid phase from a nonadsorbing solvent (trimethyl benzene) in zeolite NaZSM-5 at 10, 30, and 50 degrees C. The diffusion coefficients show a sharp decrease for molecules whose carbon chain length is larger than the channel length of the zeolite. The adsorption isomers of octane have also been studied to observe the effect of minor structural changes in molecular shape on adsorption properties in the zeolite. The observed adsorption capacity data have been explained in terms of molecular packing in zeolite straight and sinusoidal channels and channel intersections.