The sequential bond energies of Co(CH4)(x)(+), x = 1-4, are determined experimentally and theoretically. Collision-induced dissociation studies conducted using a guided ion beam tandem mass spectrometer yield 0 K bond energies of D-0[Co+-Xe] = 0.85 +/- 0.07 eV, D-0[Co+-CH4] = 0.93 +/- 0.06 eV, D-0[Co(CH4)(+)-Ch(4)] = 1.00 +/- 0.05 eV, D-0[Co(CH4)(2)(+)-Ch(4)] = 0.41 +/- 0.05 eV, and D-0[Co(CH4)(3)(+)-CH4] = 0.67 +/- 0.06 eV. These numbers are in excellent agreement with ab initio calculations which lead to values of D-e[Co+-(CH4)] = 0.93 eV, D-e[Co(CH4)(+)-CH4] = 1.00 eV, D-e[Co(CH4)(2)(+)-CH4] approximate to 0.40 eV, and D-e[Co(CH4)(3)(+)-CH4] approximate to 0.70 eV. We find that the nonmonotonic behavior in the sequential binding energies arises from changes in hybridization at the metal center as the third ligand is bound.