Polarization-dependent near edge X-ray absorption fine structure (NEXAFS) spectroscopy was used to determine the ordering of octadecyltrichlorosilane (OTS) molecules in self-assembled (SA) films on Si/SiOx. Coverages of adsorbed material for different SA films were determined by integration of the NEXAFS signal due entirely to the C 1s absorption, The structures and coverages of the SA films deposited by chemisorption from solution in toluene were determined for two different deposition conditions: (1) open to the atmosphere and (2) water- and oxygen-free conditions inside a drybox. SA films of OTS deposited under ambient air conditions grew as islands on the substrate and were well-ordered as indicated by a strong polarization-dependence in the NEXAFS spectra. For depositions performed in the drybox, ordered or disordered films grew uniformly over the substrate. Ordered SA films deposited in the drybox exhibited higher average tilt angles and lower coverages of adsorbed material than SA films deposited under ambient air conditions. The structure and coverage are discussed with respect to results from measurements of contact angles of water and ellipsometry.