Poly(ethylene terephthalate) is used in numerous industrial applications. Successful medical applications are in the area of cardiovascular surgery. Its chemical functionality makes it propitious to grafting biochemical compounds; surface modification by plasma treatment may also be used to improve biocompatibility and modify wetting properties. The analyzed specimen was a commercial film (Mylar A). The main C 1s region was decomposed into three main components which were clearly identified on the recorded spectrum: 284.8, 286.4, and 288.8 eV attributed, respectively, to carbon only bound to carbon and hydrogen [C_—(C,H)], carbon making a single bond with oxygen [C_—O] and carbon of ester [C_OO]. Satellite peaks were found at 291.3, 293.5, and 295.8 eV. The molar ratios C_—(C,H):C_—O:C_OO were 3:0.92:0.91 excluding the satellite peaks, to be compared with the expected values of 3:1:1. The O 1s peak showed two partially resolved components at 531.6 [O_=C—O] and 533.3 eV [O=C—O_] with a satellite at 538.2 eV. The O:C ratio was 27.8:72.2, to be compared with the expected values of 28.6:71.4. The FWHM of the main C 1s components was in the range of 0.90 to 1.23 eV depending on the component and the mode of decomposition; the FWHM of O 1s components was about 1.40 eV.