Neutron scattering measurements and molecular dynamics simulations have been carried out on the three isomers of pentane (neopentane (neo), isopentane (iso), and n-pentane (n-)) adsorbed in zeolite NaY. The results show that the self-diffusivity of these isomers follow the order D-s(neo) > D-s(iso) > D-s(n-), suggesting that the larger the cross section perpendicular to the molecular axis of the isomer, the higher the self-diffusivity. This counterintuitive result provides the first direct experimental evidence in support of the Mutual cancellation of forces on the diffusant leading to a diffusivity maximum and is often referred to as the levitation effect. We also provide a direct confirmation of the experimental observations by Kemball (Adv. Catal. 1950, 2, 233) by calculating the entropy.