An experiment is described which measures the fission thresholds of thermally fissionable nuclides. In contrast to fission induced by neutron capture, use of the (d, p) reaction allows compound nuclei to be produced with excitations less than the binding energy of the last neutron. Measurements of the energy spectra of protons in coincidence with fission, normalized by the energy spectra of all emitted protons, have allowed the thresholds of Pu239, U233, and U235 to be observed. It should be emphasized that the compound nucleus is stable against neutron emission in the region of these fission thresholds, thus avoiding distortions by this competing reaction. The threshold of U238 was also obtained for comparison with neutron data. In the case of the even-even compound nuclei, the observed step structure of the fission threshold is a clear indication of a multiple fission barrier. This multiple barrier is predicted by the collective model of fission and is correlated with the experimental data. The equivalent neutron energies at the center of the first threshold are as follows: for Pu239, -1.61 Mev; for U233, -1.47 Mev; and for U235, -0.60 Mev. The second thresholds are observable only for the first two: for Pu239, -0.72 Mev, and for U233, -0.72 Mev. The threshold of U238 agrees well with the data from neutron excitation. In each case the fission probability decreases in the region of positive neutron energies. This would result either if neutron emission were to compete with fission or if there were a significant contribution to the proton spectrum from the electric breakup of the deuteron.