Probing the fundamentals of oxidative coupling In their Communication on p. 2809 ff., B. Zohour, D. Noon, and S. Senkan reveal new insights into the oxidative coupling of methane. Spatial concentration profiles were measured in a La2O3/CeO nanofiber catalyst packed bed reactor using micro-capillary sampling coupled to on-line gas chromatography. These measurements revealed the early (i.e. prompt) formation of H2 in the oxidative coupling of methane (OCM) reaction, which has not been reported before. This discovery has important mechanistic implications for the development and refinement of fundamentally-based detailed chemical kinetic mechanisms (DCKM) for the OCM reaction. Once developed, DCKM are combined with the transport models for reactors to predict their behavior over a broad range of conditions, including conditions under which experimental data are not available or feasible. Consequently, DCKM play a vital role to evaluate different reactor configurations and process conditions, which are necessary to increase the yields for C2+ products, in order to bring the OCM process closer to commercial viability.