Process for the preparation of fluorinated alkanes by contacting a starting material of halogenated alkene or alkane with 1 to 150 molar equivalents based on catalyst of HF, 1 to 30 molar equivalents based on catalyst of a dehydrating agent and less than 100 molar equivalents based on catalyst of a starting material, the catalyst being selected from niobium oxide or tantalum oxide, at a temperature of 0.degree. C. to 185.degree. C. The preferred dehydrating agent is a combination of chlorosulfonic acid and thionyl chloride.