The influence of adlayer compression on the physisorption of Ar on Pt(111) is investigated using temperature programmed desorption and modulated molecular beams. We find that the difference in coverage between the compressed and uncompressed first layers is similar to10-15%. For coverages near one monolayer, this compression causes nearly temperature independent desorption kinetics over a wide temperature range (32-41 K). We present a theory that includes the effects of the compression on the desorption kinetics and explains the observed kinetics in terms of a competition between adsorbate-substrate and adsorbate-adsorbate interactions resulting in a continuous increase in the chemical potential near the completion of each successive layer. (C) 2003 American Institute of Physics.