The co-adsorption of carbon monoxide and benzene on Pt(111) has been studied by theoretical tight-binding calculations. We used the ordered (2root3 x 4) rect-2C(6)H(6)+4CO superlattice. The computed energies for the adsorption sequences agrees with the experimental fact that CO displaces benzene. A comparison of the co-adsorption with CO and benzene 2D networks and both, CO and benzene 2D, adsorbed alone on Pt(111) is also given. An important H-H intermolecular interaction between benzenes is reinforced when CO is added to the surface. In addition, the Pt-C6H6 overlaps population decrease while a bonding interaction is developed between carbon from benzene and the C and O atoms from carbon monoxide. The density of states (DOS) and crystal orbital overlap population (COOP) curves clearly show this behavior. (C) 2004 Elsevier B.V. All rights reserved.