The gas-phase reactivity of YS + , ZrS + , and NbS + towards oxygen-transferring reagents such as H 2 O, CO, CO 2 , and COS is investigated using guided-ion beam (GIB) and Fourier-transform ion cyclotron resonance (FTICR) mass spectrometry. A lower limit of D 0 (M + –S)>4.50±0.04eV for the sulfur binding energy is derived from the exothermic formation of MS + in the reaction of all three atomic metal ions, M + , with CS 2 . Upper limits for D 0 (M + –S) are determined by collision-induced dissociation of MS + with Xe. The O-transfer experiments carried out in the GIB instrument lead to several estimates for D 0 (M + –S), which are further refined by equilibrium constants K eq derived from the reaction MS + +H 2 O→MO + +H 2 S and its reverse. Overall assessment of the results from ion–molecule reactions, collision-induced dissociation, and equilibrium measurements yields the 0K bond energies of D 0 (Y + –S)=5.49±0.18eV, D 0 (Zr + –S)=5.69±0.10eV, D 0 (Nb + –S)=5.20±0.21eV, D 0 (Y + –CS)=1.42±0.08eV, D 0 (Zr + –CS)=2.67±0.11eV, and D 0 (Nb + –CS)=2.51±0.11eV, and heats of formation for Δ f H 0 (YOS + )=6.59±0.37eV, Δ f H 0 (ZrOS + )=8.45±0.33eV, Δ f H 0 (NbOS + )=9.05±0.27eV, Δ f H 0 (YS 2 + )=6.96±0.70eV, and Δ f H 0 (ZrS 2 + )=9.34±0.73eV.