Methods of dehydrogenating hydrocarbons to yield unsaturated compounds are described. Reactor configurations useful for dehydrogenation are also described. Hydrocarbons can dehydrogenationed, for relatively long periods of time-on-stream, in a reaction chamber having a dimension of 2 mm or less to produce H.sub.2 and an olefin. Techniques have been developed that reduce coke and allow stable, relatively long-term operation in small reactors.