Both direct and indirect experimental evidence indicates that nonspherical adsorbates adopt multiple out-of-plane orientations on solid substrates. Few existing models account explicity for this effect on the adsorption equilibrium and kinetics, particularly when steric blocking effects are significant. In this work, a quantitative model is developed to account explicitly for the effects of steric blocking, solute shape, affinities of the different adsorption orientations, and solute concentration on the intrinsic equilibrium behavior. The model accurately correlates experimental isotherms in both gas/solid and liquid/solid systems. The fitted adsorption capacity and aspect ratio of the solutes are consistent with the solute size, shape, and specific surface area of the adsorbent. The proposed model describes quantitatively the tendency at low surface coverage for a solute to adsorb in an orientation with the largest surface contact area (energetically favored), while at a high coverage, most adsorbed molecules are orientated with a smaller contact area (sterically favored). The transition from side-on to end-on average orientation occurs over a large range of coverage if the aspect ratio is small and the affinity of the side-on orientation is much higher than that of the end-on orientation. The model also predicts that the apparent linear isotherm parameter estimated experimentally can increase with decreasing surface coverage, resulting in a strongly nonlinear Scatchard plot. This model could be valuable both in fundamental mechanistic interpretation of adsorption processes and for accurate experimental data correlation.