Pioneer 11 observations of energetic proton acceleration in interplanetary shock are in good agreement with predictions of the V↘×B↘ electric field model of shock acceleration. The V↘×B↘ model predicts that relativistic particles are accelerated by a factor of 2–15 in kinetic energy during a single encounter with a quasi‐perpendicular (ψ≳75 °) supernova shock wave, and that the post‐encounter pitch angle distributions are very anisotropic.