Vacancy–oxygen (VO) complexes in Ge crystals have been studied by means of high-resolution infrared absorption and deep-level transient spectroscopy (Laplace DLTS) measurements. It is argued that the VO center in Ge has three charge states: double negative (VO−−), single negative (VO−) and neutral (VO0) with the corresponding energy levels at E(−−/−)=Ec−0.21eV and E(−/0)=Ev+0.27eV. Absorption lines at 716, 669 and 621cm−1 have been assigned to oxygen-related asymmetric stretching vibrations for the VO−−, VO− and VO0 states, respectively. Isotope analogues of these lines were identified in 18O-doped Ge samples and studies of crystals containing mixtures of 16O and 18O confirm that the complex contains only one oxygen atom. Laplace DLTS combined with uniaxial stress has been used to obtain information on the symmetry of the VO complex. It was found that the defect in VO−− state has orthorhombic-I symmetry (point group C2v) as for the case of the VO in Si.