A Tian-Calvet type calorimeter is applied to the simultaneous determination of adsorption isotherms and heats of adsorption. This is the first of a series of studies of the effect of adsorbate size and polarity on the energetics of adsorption in zeolites. The adsorbate gases used is this study are quadrupolar (N-2 and CO2) and nonpolar (Ar, O-2, CH4, C2H6, and SF6). The heats of adsorption of both polar and nonpolar gases are either constant or increase with coverage, so silicalite may be classified as a relativity homogeneous adsorbent compared to X type zeolite, Reversibility was established by comparing adsorption and desorption isotherms. Reproducibility was studied by comparing runs for different samples of the same adsorbent, The average experimental error in loading is +/-0.6%. The error in the isosteric heat of adsorption is +/-2% for heats lar ger than 20 kJ/mol and +/-5% for heats smaller than 20 kJ/mol.