Current transport theory is extrapolated to predict the performance characteristics of future tokamak power reactors operating in a quasi-steady-state mode. Criteria for the suppression of macroscopic instabilities are used to delimit a stable reactor regime. Microscopic instabilities are accounted for by enhancement of the transport coefficients. The effect of variations in reactor size and aspect ratio, toroidal current, injected ion source strength, and toroidal magnetic field strength are evaluated. Results are presented in terms of engineering parameters such as fractional fuel burn-up and power output.