XOS (also known as X-Ray Optical Systems) is a company that manufactures application-specific x-ray fluorescence (XRF) analyzers for renewable fuels and petroleum industries. It produces sulfur, silicon, chlorine, multi-element, and phosphorous analyzers, x-ray optics and sources, and product selectors. X-Ray Optical Systems offers service and maintenance programs and spare parts, accessories, and supplies, such as sample stands, fan filters, removal tools, pipettes, sample cups, etc.