An energy balance shows that the force required to peel an elastic film from a rigid substrate depends not only on the adhesive surface energy but also on an elastic deformation term. This elastic term, tending to reduce the adhesion force, can only be significant in two instances: for materials which can support stresses approaching the elastic modulus without fracturing, and for very small peel angles. Experiments using rubber peeling from glass over a range of peel angles support the theory.