The aim of these experiments is to investigate the physical processes involved in oxygen transfer between sediments and the surrounding fluid and to relate the suspended sediment oxygen demand to the concentration of suspended sediment. Experiments were performed in an annular flume using crushed walnut shells as a surrogate for sewage solids. Dissolved oxygen (DO) and sediment concentration were measured. The oxygen uptake was found to be a function of suspended sediment concentration and independent of DO concentration in the range measured during the experiment (between 5 mg/L and 7.5 mg/L). A suitable model to quantify this process is proposed and fitted to experimental observations.