After closure, the near-field of a nuclear waste repository contains large amounts of oxygen in tunnels and deposition holes. The bentonite buffer/backfill will contain oxygen as a gas phase in unsaturated pores as well as dissolved gas in porewater. The redox conditions in the bentonite filling after post-closure will change towards reducing conditions. In the initial stage, the development of the redox state is mainly governed by the depletion of oxygen. The main mechanisms of oxygen depletion in the bentonite are: 1) diffusion into the surrounding rock and 2) reactions with accessory minerals and by microbial aerobic consumption of organic matter [1,2]. The reactions leading to oxygen depletion are not, however, well understood. The objective of this work was to gather new information concerning oxygen depletion in MX-80. This was done by measuring oxygen depletion and changes in the redox state in suspensions of 1) MX-80, 2) a heavy fraction of MX-80, or 3) a light fraction of MX-80.