Testpieces consisting of a fabric-backed styrene-butadiene rubber (SBR 1502) layer bonded directly to polyethylene terephthalate (PET) film were T-peel tested at various rates, R, and temperatures. Peel energies were superposed to form master-curves using shift factors, a(T), in accord with the universal WLF equation. When peeled at intermediate reduced rates, Ra-T, failure was cohesive within the SBR 1502, while at sufficiently high or low Ra-T interfacial separation between the rubber and PET occurred. These results markedly contrast with those found by Gent and Petrich using similar testpieces with another type of rubber SBR 1513. They found cohesive failure at sufficiently low Ra-T and interfacial failure when Ra-T was high. The different behavior of the two elastomers is attributed to stronger interfacial attraction with SBR 1513 and its lower strength. General considerations governing the locus of failure during peel adhesion testing are discussed.