The extent of reduction of supported cobalt catalysts is difficult to determine using TPR due to the unknown stoichiometry of reduction and due to the dynamic nature of the measurement. A method is described where, by using a combined TPR/TPO technique, it is possible to determine the extent of cobalt reduction and obtain an estimate of the extent of cobalt-support species formation. The results showed that the extent of metal reduction following hydrogen reduction at 500 degrees C is affected considerably by the type of metal carrier. In particular, the extent of metal reduction decreased with increasing aluminium content of the support material. Decreasing extents of metal reduction could be correlated with an increase in the temperature required for reduction of the nitrate ion during TPR. Increasing the time and temperature of hydrogen reduction results in increased extents of metal reduction.