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Adsorption of C20-C36 linear paraffins on the amorphous microporous silica-alumina ERS-8 was studied at vapor phase and liquid phase conditions. Henry adsorption constants and low coverage adsorption enthalpies were determined using the pulse chromatographic method at temperatures between 90 and 370°C in gas phase. The low coverage adsorption enthalpy increases linearly with carbon number with 5.5 kJ/mol per additional methyl group. Competitive adsorption in liquid and dense vapor phase conditions was studied by performing column breakthrough experiments with various binary C20-C36 n-paraffin mixtures diluted in short chain length alkane solvents or undiluted as bulk mixture, at temperatures ranging from 25 to 300°C and pressures from 3 to 110 bar. Both the adsorption capacity and the selectivity are strongly temperature and pressure dependent. At low temperature and high pressure, all n-paraffins are adsorbed equally and no separation is possible. With increasing temperature and decreasing pressure, the density of the bulk phase decreases, and a transition from a pure liquid paraffin stream to a dense vapor stream occurs. In such conditions, longer n-paraffins are adsorbed preferentially compared to the shorter n-paraffins. The selectivity increases with increasing difference in chain length between the adsorbing n-paraffins.