Energy-resolved, competitive threshold collision-induced dissociation (TCID) methods are used to measure the gas-phase acidities of phenol, 3-methylphenol, 2,4,6-trimethylphenol and ethanoic acid relative to hydrogen cyanide, hydrogen sulphide and the hydroperoxyl radical using guided ion beam tandem mass spectrometry. The gas-phase acidities of Δ_acidH₂₉₈(C₆H₅OH) = 1456 + 4 kJ/mol, Δ_acidH₂₉₈(3-CH₃C₆H₄OH) = 1457 + 5 kJ/mol, Δ_acidH₂₉₈(2,4,6-(CH₃)₃C₆H₂OH) = 1456 + 4 kJ/mol and Δ_acidH₂₉₈(CH₃COOH) = 1457 + 6 kJ/mol are determined. From the Δ_acidH₂₉₈ values the O-H bond dissociation enthalpies of D₂₉₈(C₆H₅O-H) = 361 + 4 kJ/mol, D₂₉₈(3-CH₃C₆H₄OH) = 356 + 7 kJ/mol, D₂₉₈(2,4,6-(CH₃)₃C₆H₂OH) = 340 + 5 kJ/mol and D₂₉₈(CH₃COO-H) = ≤479 + 6 kJ/mol are derived. A comparison of the new TCID values with both experimental and theoretical values from the literature is presented.