An improved algorithm to construct molecular potential energy surfaces for polyatomic reactions is presented. The method uses the energies, gradients, and Hessians, which can be obtained from ab initio quantum chemical calculations. The surface is constructed by interpolating the local quadratic surfaces with reaction path weights. The method is tested with a five-atom reaction system for which an analytic potential energy surface has been reported together with classical trajectory results. An excellent agreement is achieved for energy partitioning in products obtained by trajectory calculation on the original analytic and interpolated surfaces. Reduction of error caused by the use of the reaction path weight is explained. (C) 1997 American Institute of Physics.