In the present contribution, we performed ab initio Møller-Plesset perturbation theory second-order (MP2) calculations in the framework of the supermolecule approach on the vertical excitation spectra of the weakly bound van der Waals CO-Ar molecule in its "near T-shaped" most stable ground state structure, as a guideline for future theoretical and experimental work. These test calculations indicate a ground CO(Χ1∑)-Ar( 1S) interaction with Re = 3.72 Å, De = 109cm-1 and Do = 92cm-1. They also indicate an excited CCXA1∏)-Ar(1S) interaction with Re = 3.55 Å, De = 141cm-1 and Do = 121cm-1. A red shift of 29cm-1 for the CO(Χ1∑))-Ar(1S)→CO(A1∏)- Ar(1S) vertical excitation energy, with respect to the corresponding CC(Χ1∑) → CO(A1∏) excitation in the absence of Ar, can be obtained by comparing the corresponding Do values.