An experimental technique is demonstrated, in which the spatial variations of temperature inside a diesel oxidation catalyst (DOC) can be measured during an NEDC drive cycle. This leads to the development of a methodology which enables more scientific measurements to be performed on such a catalyst when it is connected to a live diesel engine. During hot and cold start NEDC drive cycles, measurements were performed on a Pt on alumina DOC connected to a Ford 2.0 litre diesel engine. Under these transient conditions, emission data was gathered (pre- and post-DOC), and this was also translated into cumulative emissions over the drive cycles. In addition, valuable data was gathered on the spatial temperature variations in the DOC during such a drive cycle and it is shown how, under certain conditions, the temperatures start to increase at the back-end of the catalyst and then move towards the front. This data, in combination with other measurements, helps to understand the performance of the DOC and can also be used to test the robustness of mathematical models of such systems.