Controlled reduction of MoO3 can produce different phases of catalytic interest. One of these phases has been considered as being an oxycarbide of molybdenum. Various techniques mainly TEM but also XRD and others have been extensively used to understand the mechanism of formation and the structure of this oxycarbide. Its structure is reminiscent of the MoO3 structure as shown by XRD, but reconstructed by shear planes and the introduction of carbon atoms to fill oxygen vacancies, both blocking the formation of MoO2 the normal product of the slow reduction of MoO3. The HRTEM pictures showed a ’chevron-like’ arrangement and the electronic microdiffraction a square lattice reminiscent of the (OkO) planes of MoO3.