By measuring the relative yields of alkenes and oxygenated products when n-C4H10, but-1-ene, and cis- and trans-but-2-ene, are added to slowly reacting H2+ O2+ N2 mixtures at 480°C, overall velocity constants have been obtained for the reactions of n- and s-C4H9 radicals with O2 to give 1,2-epoxybutane, cis- and trans-2,3-epoxybutane, methyl ethyl ketone and tetrahydrofuran. Mechanisms for the production of CH3CHO, C2H5CHO and CH3COCH3 from n-C4H10 are discussed and evidence favouring the reaction of alkylhydroperoxide radicals (QOOH) with O2 is presented. Comparison of the relative yields of 2,3-epoxybutane and C4H8–2 provides strong evidence that conjugate alkenes are formed directly from R + O2, or from RO2, rather than from QOOH. On this assumption, velocity constants for 1,3 to 1,6 isomerisations of RO2→ QOOH for primary, secondary and tertiary hydrogen atom abstraction have been suggested. The values suggest that the activation energies are significantly different from those previously suggested.