We have performed a benchmark study of molecular O-2 binding on Au-n (n = 1-3) clusters using density-functional theory and high-level coupled-cluster calculations. Based on the computed structural and energetic properties of O2 binding on anionic, cationic, and neutral Aun (n = 1-3), we find that the hybrid functionals (HSE06, PBE0, and B3LYP) and the M06 functional with large basis sets give much more reasonable binding energy of O-2 and O-O bond length compared to GGA functionals (PBE and TPSS). In particular, the HSE06 functional gives the best agreement with CCSD(T)//MP2 method in O-2 binding energy on neutral Au-3. (C) 2013 Elsevier B.V. All rights reserved.