A p-adaptive scheme is developed in order to overcome volumetric locking in low order finite elements. A special adaptive scheme is used which is based on the partition of unity concept. This allows higher order polynomial terms to be added locally to the underlying finite element interpolations basis through the addition of extra degrees of freedom at existing nodes. During the adaptive process, no new nodes are added to the mesh. Volumetric locking is overcome by introducing higher order polynomial terms in regions where plastic flow occurs. The model is able to overcome volumetric locking for plane strain, axisymmetric and three-dimensional problems.