Adsorption isotherms for triethylamine and tributylamine solutions in toluene onto AgI in the very dilute region are presented and treated according to Everett, and Sircar and Myers models. An analysis of molecular orientation in the adsorbed phase and its consequences on the calculated cross-sectional areas for adsorbed molecules is performed, and a simple procedure to calculate cross-sectional areas along different molecular projections, based on basic geometrical shapes, is put forth. The proposed procedure is tested for the adsorption of alkanoic acids on silica and leads to results identical with Meyer＇s. For spherical molecules the values compare well with those of McClellan and Harnsberger. Finally, the contribution of these new cross-sectional values to attain a set of coherent quantities from the adsorption experiments is revealed.