A spinel forming castable with an initial MgO content of 8%, commonly applied in refractory linings in the steel industry, was characterised with regard to the creep behaviour. Three creep stages were observed for 1300, 1400, and 1500 °C for application relevant loads between 3 and 8 MPa for sintered samples. The parameters of the Norton–Bailey creep model were determined for all three creep stages. The added microsilica increased the creep strain rate in the temperature range above 1300 °C. The fitting of the results for only one temperature carries the risk of over-fitting. This was observed for the first creep stage at 1400 and 1500 °C. Nevertheless, for the investigated material, it was not possible to achieve a common fit for a larger temperature range. The evaluation of the creep parameters by different combinations of measurements allowed to obtain statistical information about the creep parameters.