Despite many experimental and theoretical studies, the crystal structure of the epsilon phase of solid oxygen has not been determined. We performed powder x-ray diffraction experiments and the Rietveld analyses in this study to show that a new arrangement of the monoclinic space group C2/m could fit the diffraction patterns of the epsilon phase and obtained a structure that consisted of an O8 cluster with 4 molecules. The dependence of the lattice parameters, the molar volume, and the intermolecular distances on the pressure was investigated.