The formation of self-assembled alkanethiolate monolayers (SAMs) on oxidized gold was studied by X-ray photoelectron spectroscopy (XPS), contact angle measurements, and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. Gold was oxidized by exposure to atomic oxygen in a vacuum. SAMs were prepared by two methods: (a) by immersion of the oxidized substrate into ethanolic solution and (b) via chemical vapor deposition (CVD). After both procedures two sulfur species could be distinguished by XPS, a gold thiolate and a species related to the reaction of the thiol with oxidized gold. Oxygen was found encapsulated under the self-assembled monolayer. The monolayers adsorbed from ethanolic solution were more densely packed and exhibited a smaller molecular tilt than the layers formed by CVD or SAMs prepared on clean gold surfaces.