The output signal of a pre-catalytic converter lambda probe and the output signal of a controller are used to determine an inherent delay time of the pre-catalytic converter lambda probe, for example due to aging of the probe, by measuring, for example, the separation between maxima in these output signals. The pre-catalytic converter lambda probe is installed in an exhaust gas system of an arrangement wherein an internal combustion engine operated under controlled conditions. The determined delay time can be used to determine the oxygen storage capacity of an oxygen store associated with a catalytic converter in the arrangement by determining with the pre-catalytic converter lambda probe the start of a time interval over which integration takes place, and determining the actual end time of the integration by adding the delay time to an end time determined from an output signal of the post-catalytic converter lambda probe.