The variational normal coordinate code 'Multimode' has been used to predict the zero point, fundamentals and overtones of the 30-mode system, benzene. One through 4-mode integration coupling has been included. Vibrational self-consistent field and configuration interaction results have been obtained; they are compared with those of perturbation theory. These calculations demonstrate that 'Multimode' can be used to study the vibrational motion of larger molecules; furthermore we have shown that the degree of coupling can be used to predict the convergence of the vibrational levels. (C) 2002 Elsevier Science B.V. All rights reserved.