Isotherms of five n-alkanes: propane, butane, pentane, hexane, and heptane in 13 X zeolite have been measured by microgravimetry. In temperature ranges in which the isotherms are reversible, the sorption is described by the statistical model developed by Dupont-Pavlovsky, showing that the sorbed phase is localized. The heat of sorption and the sorbate-sorbate interaction, obtained from the model, increase with the number of carbons.