The systematic data on the effect of ribbing on the parameters of a relative (in comparison with a smooth channel) increase in hydraulic resistance εp and heat transfer εq in the range of Reynolds numbers from 50 to 8∙106 has been obtained by numerical modeling of a developed spatially periodic flow and stabilized heat transfer of incompressible gas with a Prandtl number of 0.7 in a rectangular channel with one-sided internal ribbing. In the laminar regime, the εq value was found to be small and amounted about 10%, and εp value exceeding 2.5. In the turbulent regime, the εq value behaved nonmonotonic depending on the Reynolds number, the range of its variation was 1.5–2.6, while εp increased from 3.5 to 7.0.