to gain better understanding of reactions as gas composition and temperature changes within a catalyst. These recent advances in sampling techniques offer previously unavailable insights in terms of kinetics and surface processes within the sample. The development of techniques using in-situ probes are providing the opportunity to bridge the "knowledge gap" between traditional catalyst effluent analysis and theories, and provide the additional information which is required to improve relevant simulations and models. However, there are several aspects in this evaluation of in-situ probes [1] which need to be examined in greater detail.