Nine minima were found on the intermolecular potential energy surface for the ternary system HNO3(CH3OH)(2) at the MP2/aug-cc-pVDZ level of theory. The cooperative effect, which is a measure of the hydrogen-bonding strength, was probed in these nine conformations of HNO3 center dot center dot center dot(CH3OH)(2). The results are discussed here in terms of structures, energetics, infrared vibrational frequencies, and topological parameters. The cooperative effect was observed to be an important contributor to the total interaction energies of the cyclic conformers of HNO3 center dot(CH3OH)(2), meaning that it cannot be neglected in simulations in which the pair-additive potential is applied.