The packing arrangements of selected hydrocarbons in AlPO4-5 molecular sieves were proposed. These molecules were of sizes comparable to the pore diameter of AlPO4-5. These packing arrangements at least qualitatively explained the results on vapor adsorption, liquid-phase counter diffusion, and binary liquid adsorption. Ortho-xylene behaved differently from its isomers in adsorption and diffusion processes. Its packing arrangement also reflected this fact.