For decades, water and oil repellency of engineering thermoplastics has been achieved with introduction of long-chain perfluoroalkyl substances and moieties (CnF2n+1, n >= 7). However, their bioaccumulative and toxicological impact is now widely recognized and, consequently, the substances have been phased out of industrial production and applications. To this end, we have synthesized fluorinated oligomeric triblock polyesters (FOPBs), which do not possess the long chain perfluoroalkyl segments and serve as effective low-surface-energy additives to engineering thermoplastics. More specifically, we obtained original perfluoropolyether (PFPE)-based triblock copolymers, in which two identical fluorinated blocks were separated by a short nonfluorinated polyester block made of poly(ethylene isophthalate) (PEI). It was found that when FOPBs were added to poly(ethylene terephthalate), nylon-6, and poly(methyl methacrylate) films they readily migrate to the film surface and in doing so imparted significant water and oil repellency to the thermoplastic boundary. The water/oil wettability of the films modified with FOPB is considerably lower than the wettability of the films modified with an analogous PFPE-based polyester, which differs from FOPB only by the absence of the short nonfluorinated PEI middle block. We associate the superiority of the triblock copolymers in terms of water and oil repellency with their ability to form brushlike structures on polymer film surfaces.