Scanning Probe Microscopy (SPM) has been utilized to study the adhesive behavior of a blend of poly(ethylene propylene) (PEP) and the n-butyl ester of abietic acid. This blend is a model for a pressure sensitive adhesive (PSA). Force-distance measurements with simultaneous X-modulation gave information on both lateral and normal force during loading and unloading. This was a key advantage of the approach. The mechanism of adhesive failure has been elucidated by comparing the dependence of pull-off force (Fpull-off) and oscillating lateral force (F-lateral) on velocity of loading/unloading and by studying the change with velocity in the loss of effective contact area during debonding. Change in contact area with time was inferred from change in the rms lateral force. The velocity dependence of F-lateral indicates that its magnitude is strongly influenced by both contact time and the presence of tackifier. In contrast, the velocity dependence of Fpull-off is controlled by both the loading and unloading processes. While the adhesive behavior of the polymer (PEP) was mainly controlled by chain stretching during the unloading process, the adhesive performance of the tackifier enriched surface (PEP/60) was determined by the loading process at 10-50 nm/s loading velocity and by the unloading process at 100- 1000 nm/s velocity. (C) 2004 Elsevier Ltd. All rights reserved.