The quantitative prediction of catalyst selectivity is essential to the design of efficient catalytic processes and requires a detailed knowledge of the reaction mechanism and rate constants. Here we present a study that accurately predicts, using the kinetics and a mechanism derived from fundamental studies on single-crystal gold, the product distribution resulting from the complex reaction network that governs the oxidative coupling of methanol, catalysed by nanoporous gold between 360 and 425 K and for a vast range of pressures. Analysis of the transient product responses to micropulses of methanol over nanoporous gold yields a precise understanding of the marked dependence of selectivity on pressure, surface oxygen coverage and temperature. The key to a high selectivity for methyl formate is the surface lifetime and abundance of the methoxy. This successful microkinetic modelling of catalytic reactions across a wide set of reaction conditions is broadly applicable to predicting catalytic selectivity and provides a pathway to designing more efficient catalytic processes. Catalytic studies on single crystals are very insightful, but it is often difficult to extend their conclusions to an actual catalytic process due to gaps in the experimental conditions. Now, Madix and co-workers report a method to bridge these gaps using the oxidative coupling of methanol on gold as an example.