The reactions of B+ + CH4 + nH2 (n = 1, 2) to produce B+ sigma-bonded insertion products have been studied by high-level ab initio computational techniques. The results demonstrate that the mechanism of sigma bond activation by cooperative interaction, previously identified for the B+ + nH2 and B+ + nCH 4 systems, continues to operate for the B+ + CH 4 + nH2 systems. In the mixed systems, the CH and HH sigma bonds compete for the role of the "insertion" sigma bond or the "cooperating" sigma bond and CH4 can alternatively participate as a one or two sigma bond contributor. Although the transition state separating electrostatic complexes from covalently bound B+ insertion products may appear to favor CH insertion (n = 1) or HH insertion (n = 2), the activation energy required to convert these products is only about 20% of the available exoergicity, so that both products would be expected in practice. Remarkably, the reaction of B+-(H2)2 + CH4 is predicted to proceed to B+ insertion products with an activation energy of less than 1 kcal/mol.