A modified version of the Shepard interpolation scheme proposed recently by Collins ct al. is used to determine a potential energy surface for the H-2-H reaction. Our modifications are based on preliminary calculations in which the Liu-Siegbahn-Truhlar-Horowitz surface for H-3 is used to study convergence of the Shepard procedure. Included in the modifications are changes to the form of the weight functions, the coordinate sets used in the zeroth-order surface, and the transformation of the Cartesian first and second derivatives to internal coordinates. The new ab initio potential energy surface is based on calculations using the basis set of Siegbahn and Liu and second order Moller-Plesset (MP2) perturbation calculations. We have not experienced convergence problems with the self-consistent-held iteration while ''growing'' the surface. Furthermore, a converged fit can be obtained using only 85 ab initio calculations. This demonstrates that the Shepard interpolation scheme is a powerful candidate for automatic determination of medium quality potential surfaces for dynamical calculations. (C) 1997 American Institute of Physics.