Deformations of CO2, CO2+, and CO22+ in intense laser fields (> 10(14) W/cm(2)) are investigated by using potential energy surfaces of field-following adiabatic states at various instantaneous field strengths. The adiabatic states are obtained by ab initio molecular orbital calculations. To predict tunnel ionization of multi-electron molecules, we propose a new approach based on the idea that electron transfer induced by an intense laser field charges each atom in a molecule and that ionization proceeds via the most negatively (or least positively) charged atomic site. We conclude that bond stretching in CO22+ accompanied by large amplitude bending motion is responsible for the experimentally determined geometrical structure of Coulomb explosion species CO23+, namely, that the C-O bond length is stretched to about 1.6 Angstrom and the mean amplitude of bending is relatively large (similar to 40 degrees).