An ab initio quartic force field calculated from a cc-pVTZ basis set at CCSD(T) level of theory is used to compute the vibrational energy levels of diphosphorus oxide, P2O, in the range 200-2000 cm(-1). The most important vibrational configurations, constructed from harmonic vibrational wavefunctions, selected by an iterative process by means of a variational perturbational method are diagonalized. The results show a good agreement with the most reliable experimental values such as upsilon (3), the upsilon (1) + upsilon (3) <-- (1) hot band and two postulated Fermi resonances and predict unobserved overtones and combinations bands in the medium IR region.