Classical trajectories have been calculated for the unimolecular dissociation reaction HFCO --> HF + CO over a modified form of the potential energy surface of Wei and Wyatt (J. Phys. Chem. 1993, 97, 13580). To ensure the proper asymptotic state of the reaction products and to avoid unphysical areas in the potential energy function, HF and CO two-body potentials, an elaborate range function, and switching functions were introduced into the original analytic function. The initial rotational energy was set to zero. The total vibrational energy was between 68.7 and 73.4 kcal/mol. Clear evidence of mode specificity was found in that the excitation of the six different modes (with approximately equal total energy) gave significantly different rates of decay : CH stretch > CH bend > CF stretch much greater than CO stretch > out-of-plane bend > OCF bend.