Dissolved oxygen concentrations were monitored at 12 points distributed over 3 depths in one out of six cages in an Atlantic salmon farm and compared to the output of a mathematical model using the advection-diffusion equation and a model of the salmon's oxygen consumption to estimate spatial oxygen distributions. The effects of oxygen consumption in neighbouring fish cages on the oxygen levels observed in the monitored cage were found to be significant, and several model variants modified to better represent the real system were tested. Position data from 8 fish in the cage equipped with acoustic telemetry tags was used to refine the model configuration.Results show that simulating the full farm with all cages improves model fit significantly over simulating a single cage only. Even better fit was achieved in a single cage model with ad hoc modifications, indicating that there are additional non-modelled effects that should be investigated further. This study establishes the oxygen model as a suitable tool for monitoring and forecasting of oxygen conditions in salmon cages, and gives indications about he accuracy and limitations of the model.