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In order to obtain a deeper understanding of the performance of a diesel oxidation catalyst (DOC), techniques are developed which help to bridge the gap in the development of catalyst technology from the laboratory bench-top to an application on a real 2.0 litre diesel engine. The methodology is illustrated using a full-scale DOC (106 mm diameter; length 114 mm), from which sections are cut and then examined using a variety of techniques, including: optical measurement, SEM, TEM, FTIR, CO chemisorption, pore size and pore volume measurements. These provide valuable information on the characteristics of the Pt catalyst, in the actual form (on supportlwashcoat) that it will be used in a commercial application. In addition, a transient chromatographic technique was tested to measure the effective diffusivity in the washcoat layer. These experiments were performed using sections of v-alumina washcoated (:::::50/lm thick) monolith (1 mm channels), which were mounted in a 570 mm long housing - unfortunately this did not work. The technique was improved, and short sections of monolith, with a larger channel diameter (2.64 mm) and with a thicker washcoat (:::::475/lm) were mounted in a 1 m long sleeve - although better results were obtained, this technique still needs to be improved. A methodology was then described, in which a short section of DOC (5 mm long) was cut from the full-scale DOC, and this was connected to a live 2.0 litre diesel engine. It was shown how experiments (with gas inlet temperatures varying from 150 to 270 QC) can be performed, and in combination with a modelling technique, the information gathered can be used to test the validity of rate expressions. It was shown: (a) that the Langmuir-Hinshelwood-Hougen-Watson (LHHW) form of rate expression is clearly unsuitable for transient simulations, whereas mechanistic forms can provide a better match to the experimental data, and (b) how to tune the coefficients to match points of ignition-extinction in the light-off hysteresis cycle.