For given maximum surface and internal fuel temperatures and coolant inlet temperature, the optimum degree of artificial roughening of the surface of gas-cooled fast reactor fuel elements is such that the Stanton number is approximately doubled with respect to smooth rods. For given coolant temperatures and maximum clad temperature, the power per unit length of rod increases approximately linearly with increasing Stanton number. Core performance is not sensitive to possible uncertainties in friction factor (±25%), slight decrease in surface heat transfer, or to the fraction of the active rod which is roughened. By proper design, fuel cycle costs remain low (0.5 to 0.6 mil/kWh) for a substantial range of values of maximum clad temperature (600 to 700°C), maximum linear rating (12 to 18 kW/ft), and degree of surface roughening (1.5 to 2.5) with helium cooling of oxide rods.