To accurately describe the confined behavior of hydrocarbons in nanopores has become a top priority for the effective development of unconventional resources. In this paper, the multicomponent potential theory of adsorption (MPTA) is coupled with the cubic Peng-Robinson (PR) equation of stare (EOS) to investigate and represent the confined behavior of pure hydrocarbons and their mixtures in organic nanopores. In this theory, the fluid fluid interactions are modeled by the PR EOS. For the fluid-solid interactions, the 10-4-3 Steele potential is used for slit-like nanopores, and a modified Lennard-Jones (LJ) 10-6 potential is used for cylindrical nanopores. Then a prediction process for the behavior of methane, ethane, propane and their mixtures (binary and ternary mixtures) is performed. The results are compared against experimental data on the adsorbents of activated carbons (slit-like nanopores) and MCM-41 silica (cylindrical nanopores) to validate the accuracy of the theory and process. Results indicate that for the sets of experimental data considered in this work, the theory is capable of predicting the confined behavior of pure components in wide ranges of pressure and temperature. For pure components, because of the different interaction energy between fluids and solid walls, the density of confined fluids in the slit-like nanopores (activated carbon type) is much higher than that in the cylindrical nanopores (MCM-41 silica type). As a position (z) approaches the pore surface, the effect of fluid-solid interactions is enhanced, and the density of confined fluids is increased. For binary mixtures, the mole fraction of the heavier component (C2H6/C3H8) around the pore surface is extremely higher than that of the lighter component (CH4). The higher the difference between the two components, the higher the difference of the mole fractions and fluid densities of the two components in nanopores. For a ternary mixture, the confined behavior of the three components within nanopores is significantly different. As a position approaches the pore center, the mole fraction of the lightest component is increased gradually, and the mole fraction of the heaviest component is reduced gradually. The medium component shows a tendency of increasing first and reducing then. This investigation makes it possible to get some new insights on the confined behavior of hydrocarbons in nanopores with different geometries. (C) 2016 Elsevier B.V. All rights reserved.