The industrial application of the Plowshare concept of current interest is the stimulation of natural gas. The degree of success of this and other applications may be significantly affected by the amount of tritium produced by the nuclear explosion. The reduction of residual tritium has been the subject of continuing research and evaluation. Both public safety and economics are considered in planning this reduction. Tritium is produced from two major sources: the explosive itself and the material and rock surrounding the explosive. The improved design of the low-residual-tritium Plowshare underground engineering explosive represents considerable progress in the reduction of the amount of tritium formed. This is shown by the decrease in the total tritium produced in the 29-kt Gasbuggy event from about 40 000 Ci to the estimated <1000 Ci per 30-kt explosive for the Rio Blanco event. Neutron shielding can reduce the amount of tritium formed external to the explosive. Various compositions of borated polyethylene and other neutron-absorbing and moderating materials were investigated. Polyethylene borated at 10 to 25 at.% appears to be best suited for use as an external shield with the Diamond family of explosives, depending upon the specific rock composition. It was found that, in addition to the shielding composition and the lithium content of the rock, the effective temperature of the rock at the time of neutron absorption is very important in determining the tritium production. As an example, the proportion of neutrons undergoing tritium-producing reactions in the Gasbuggy rock changes from to when the neutrons are absorbed at energies of 1 e V and 1 keV, respectively. A sample case was calculated in which it was found that a 2.5-cm-thick shield of borated polyethylene reduced the total amount of tritium formed in the shield and rock by a factor of 2 over the unshielded case. A 10-cm-thick shield reduced the total tritium formed by an order of magnitude.