A dehydrogenation reaction of the form A double left right arrow B + H-2 was simulated in a cocurrent, isothermal, membrane-enclosed catalytic reactor to study the effects of reactant permeation rate, hydrogen-permeation selectivity, feed composition, and reactant space times on reaction conversion. Two dimensionless numbers, the Damkohler number and the permeation number, were used to quantify the effects of reactant space time and reactant loss on conversion respectively. The Damkohler number is the ratio of maximum reaction rate to inlet reactant flow rate, and the permeation number is the ratio of maximum reactant permeation rate to inlet reactant flow rate. For reactant space times at STP between 0.3 and 30 s, and hydrogen-permeation selectivities between 3 and 1000, conversion decreased as the maximum reactant permeation rate exceeded the inlet reactant flow rate because reactant loss controlled conversion. For hydrogen-permeation selectivities between 3 and 40, a membrane reactor gave maximum conversions when the maximum reactant permeation rate equaled the inlet reactant flow rate, and the reactant space times at STP had to be greater than 1.5 s to obtain conversions higher than the enhanced equilibrium conversion due to dilution by the inert sweep gas.