The synthesis of (per)fluoropolyether phosphate esters prepared by the reaction of phosphorus pentoxide and fluorinated alcohols has been investigated. The reactivity strongly depends on the structure of the fluorinated alcohol, generally decreasing with increasing acidity. Moreover, the addition of a modulated amount of water to the starting fluorinated alcohol allows the fine-tuning of the monoalkylester and dialkylester contents in the final products. Therefore, when difunctional perfluoropolyether macromonomers are considered, the polymerization degree can be varied, and phosphate oligoesters of different molecular weights can be obtained in high yields, even if, as in this study, the synthesis is focused on low-molecular-weight oligomers. This easy control of the oligoester composition in the final product makes it possible to address the synthesis of phosphate oligoesters having a well-defined equivalent weight, which also depends on the average molecular weight of the starting alcohol. The full characterization of the products is made possible by the combination of different NMR techniques (H-1, F-19, P-31, C-13, and two-dimensional NMR: P-31-H-1 and P-31-C-13). This synthetic route shows great potential and opens the way to a new family of interesting candidates for the treatment of different organic or inorganic substrates to impart phobic properties against both polar and apolar substances. (c) 2005 Wiley Periodicals, Inc.