Excited states in the proton-unbound nucleus Lu-151 have been established using gamma-ray coincidence techniques. The lifetime of the first excited state above the proton-emitting ground state has been measured using the recoil-distance Doppler-shift method combined with recoil-decay tagging. The experimental level scheme and extracted lifetime have been compared with state-of-the-art theoretical calculations based upon a non-adiabatic deformed Woods-Saxon potential. This comparison suggests that the proton-emitting ground state in Lu-151 is mildly oblate with a deformation beta = -0.11(-0.05)(+0.02) and represents best evidence to date for proton emission from an oblate nucleus. (C) 2013 Elsevier B.V. All rights reserved.