Chemical reactions with large activation energies present difficult control problems because of the rapid increase in the reaction rate as the temperature increases. This paper explores the impact of activation energy and reactant concentration on both the steady-state economics and the dynamic controllability of a process in which an exothermic, irreversible, gas-phase reaction A + B --> C occurs in an adiabatic tubular reactor. A gas recycle returns unconverted reactants fi om the separation section. Steady-state economies favor the use of high reactant concentrations, but dynamic controllability favors having the concentration of one of the reactants low, particularly with large activation energies. Two control structures are explored, one with the limiting reactant concentration controlled by fresh feed and the other with this fresh feed fixed. The first structure is only effective with low activation energies. The: second handles large activation energies, but only when reactant concentrations are not high.