The adherence of an acrylic tape on silicone elastomers containing various quantities of a silicone MQ resin has been investigated by an instrumented peel test, along the lines of Newby and Chaudhury's work (Langmuir 1997,13,1805-1809; Langmuir 1998,14,4865-4872), which gave the first evidence of interfacial slip when a pressure-sensitive adhesive is peeled from a thin poly(dimethylsiloxane) (PDMS) layer. In the present study, we show that the amplitude of interfacial slip movements is correlated to the composition of the elastomer in MQ resin (small silica-like particles inserted into the elastomer). High slip amplitudes are associated with low MQ resin content and result in weak shear deformations in the adhesive. Thus, depending on the composition of the elastomer, the peel energy is dominated either by frictional losses associated with slip at the interface (low MQ resin content) or by viscous dissipation due to shear deformations distributed in the volume of the adhesive (high MQ resin content). The transition between these two processes depends on the contact time between the acrylic tape and the elastomer prior to peeling. The viscous and the frictional parts of the dissipated energy are quantitatively estimated from the observed displacements at the interface and within the adhesive, the shear modulus of the adhesive, and frictional laws determined from "pure" shear experiments. The computed energies can represent half of the measured peel energy for this adjustable slip system. The understanding of the molecular mechanisms involved should help in the design of surfaces with adjusted adhesive properties.