Fumigant compositions including hexafluoropropene or 1,1,3,3,3-pentafluoropropene, and methods of preparing such compositions, are provided herein. The fumigant compositions may be suitable for use as soil fumigant compositions and structural fumigant compositions against a variety of undesirable species such as weeds, nematodes, pathogens, animals and insects. The fumigant compositions also have low toxicity and low Global Warming Potential.