The topotactic mechanism for the reduction of MoO3 to MoO2 has been well-supported by experiments, though the detection of Mo4O11 during the process has been a challenge to the notion of direct conversion. In this study, high quality in-situ Neutron Powder Diffraction (NPD) has been used to monitor phase composition during the reduction Of MoO3 in a flow of hydrogen at 550 degreesC. Three phases have been detected: MoO3, MoO2, and Mo4O11. Multiphase Rietveld refinement has been used to obtain concentration profiles for all three oxides throughout the reduction process. Examination of these profiles reveals the following: (1) a higher content, initially, of MoO2 than Mo4O11; (2) a period of constant MoO2 content; (3) an induction period of Mo4O11 formation; and (4) a resumption in growth of MoO2 but with different unit cell dimensions.