A process for alkylating a phosphorus-containing compound to provide an alkylated phosphorus-containing compound is provided which comprises alkylating 5 phosphorus-containing compound possessing at least one phosphorus-hydrogen alkylatable site with reactant which generates alkene and/or cycloalkene alkylating agent in situ in the presence of initiator, the alkylene and/or cycloalkylene alkylating agent alkylating the phosphorus-containing component to provide alkylated phosphorus-containing product.