The relative rates of consumption of hydrocarbon and H2 have been determined when small amounts of C3H8, n- and i-C4H10 have been added to slowly reacting mixtures of H2+ O2 in aged boric-acid-coated vessels at 480°C. Interpretation of the results enables the velocity constants for attack of H and OH on RH to be determined at 480°C, and these values have been combined with measurements at lower temperatures to give overall Arrhenius' parameters. For C2H6 and these three hydrocarbons, the velocity constants appear to be additive, and Arrhenius parameters per C—H bond for attack at primary, secondary and tertiary positions have been obtained. Upper limits for the velocity constants for HO2 attack have also been estimated.