A laboratory-scale slab burner has been used to characterize the regression rate of three different binder compounds with oxidizers varied from 100% fluorine to 100% oxygen. The oxidizer flow rate and pressure were varied from 0.014 to 0.17 lb/in.2-sec and 20 to 160 psia, respectively. In the regions of low flow rate, the regression rate was independent of pressure and increased as the 0.8 power of the specific total flow rate for each of the propellant formulations studied. At the higher flow rates, the regression rate was nearly independent of flow but increased markedly with pressure. Increasing the percent oxygen resulted in a reduction in the regression rate. The classical hybrid regression rate law was extended to include the effects of condensed-phase surface products and nonunity Prandtl number. Agreement between experimental and predicted regression rates was good in the low flow-rate regions where regression rates were independent of pressure. However, the classical turbulent heat-transfer model did not account for the observed pressure dependence of regression rate in the high flowrate regions. Rate-limiting chemical kinetic processes were postulated as the most likely cause of the observed pressure dependence.