A study of atmospheric, dissipated-vacuum and sustained-vacuum fumigation was made to determine the relative value of each. In an empty fumatorium where penetration of the fumigant is not a factor, atmospheric fumigation is almost as efficient as dissipated vacuum, but neither is as effective as sustained-vacuum fumigation. When penetration of the fumigant into soil, burlap sacking, etc., is required, sustained-vacuum fumigation is much more effective than either atmospheric or dissipated-vacuum fumigation. The difference between dissipated-vacuum and atmospheric fumigation is not so great. A higher concn. is required to penetrate moist soil than dry soil. When both adsorption and penetration to some extent have to be considered, the difference between atmospheric, dissipated-vacuum and sustained-vacuum fumigation is not so great as when penetration is the only factor to be considered.