The reaction enthalpies for the recombination of carbon-centered radicals, R, with molecular oxygen have been established by photoacoustic calorimetry (PAC) in the liquid phase and by means of density functional theory calculations (DFT) with the B3LYP functionals and the 6-31(d) basis set. The experimental study revealed the following carbon-oxygen bond dissociation enthalpies, BDE(R-OO) (kcal mol(-1)): cyclohexadienyl (12), 1-tetrahydrofuryl (32), and dioxanyl (34). For 1-triethylaminyl and 1-pyrrolidinyl, the reaction enthalpy suggests that in organic solvents disproportionation becomes important even within the first stage of the reaction. DFT underestimates the BDE(R-OO) by 0-6 kcal mol(-1). However, DFT BDE(R-H)BDE(R-OO) are in accordance with experimental data. The computed BDE(R-OO) is not sensitive to substitution by alkyl groups.