High-energy resolution X-ray photoelectron spectroscopy, with full width at half maximum of 0.41 eV for the Si 2p and of 0.54 eV for the Ge 3d, has been used to study the valence band offsets of different strained Ge layers grown on Si (100). The fractional volume changes in Ge epilayers have been measured by X-ray photoelectron diffraction and are used to correct the valence band maximum shifts caused by strained-induced spin-orbit splitting at the maxima. Band offset values of 0.80, 0.76, and 0.71 eV are found for Si/(Ge5Si5)/Si (100), Si/(Ge4Si4)/Si (100), and Si/(Ge0.5Si0.5)/Si (100) epilayers, respectively.