The life of structural members that experience cyclic loading is improved by the introduction of surface compressive residual stresses. A high-pressure oil jet is used for the introduction of surface compressive residual stresses in aluminum alloys, AA6063-T6 and AA6061-T4. The peening machine designed and developed in the laboratory is capable of generating high pressures using hydraulic oil. The magnitude of residual stress developed depends upon the stand-off distance and yield strength of the material. A hardened layer up to a depth of about 350 mu m was developed in the materials investigated. The residual stresses and surface hardening induced are comparable to that produced by other peening processes. An analytical model is proposed to predict the impact pressure. (c) 2006 Elsevier B.V. All rights reserved.