This work aims the development of a method which gives the approximate solution of product form closed queueing networks. The starting point is the integral representation of the normalization constant G. This approach has been used, for the first time, by Mitra, et al. Here is proposed a conceptually simpler solution. It follows that the memory space requirements are dramactically reduced and the processing time is quite small, even on eight bit personal computers. An important feature of this approach is that the complexity does not grows with the number of chains (classes), but only with the number of non infinite server (IS) stations.