In the search for catalysts to be utilized in a new generation of catalytic gas turbine combustors it is not unusual to hear of catalysts that appear to have worked well in a laboratory environment but do not do so when installed in a high pressure pilot-scale rig. The influence that interphase and intraphase transport limitations may have on the rate of catalytic combustion of methane in a monolith reactor (with a 1.1 mm cell size) is investigated at a Reynolds number, Re = 10(3) (with P = 2 bar) and at Re = 10(4) (with P = 15 bar), for bulk gas temperatures varying from 623-873 K and at a bulk methane mole fraction of 0.02. It is shown that it is not an easy task to evaluate chemical kinetic expressions at conditions which truly represent even the first stage (e.g., at gas temperatures from 623-973 K) in a catalytic gas turbine combustor, for as reaction rates become very fast, interphase and intraphase transport limitations also become significant, e.g., when comparing reaction rates evaluated at incorrectly assigned conditions, then even at a relatively low bulk fluid temperature = 773 K, errors may vary from ca. 35% to 80% for Re = 10(4) and 10(3) respectively. In a laboratory test environment, where experiments may be performed close to atmospheric conditions, it is also shown that it is easy to over-temperature and hence damage the catalyst, and draw false conclusions about the catalyst being too active, e.g., considering interphase resistances alone, at a bulk fluid temperature of 773 K and Re = 10(3) the catalyst is damaged, whereas at Re = 10(4) this would not have occurred. As catalyst surface temperature exceeds 800 K, intraphase diffusion may become significant and the effectiveness factor soon becomes very much less than one. Therefore, reactor scale-up should be based on calculations where the combined effects of interphase and intraphase transport processes are coupled with reactions; scale-up based on simple multipliers, e.g., those derived from residence time or gas hourly space velocity, are unlikely to work. Modelling is shown to have an important role in catalyst and system design; if applied correctly, system development costs may be reduced.