This method is for the determination of silicon (Si) in petroleum liquids using an Inductively Coupled Plasma - Optical Emission Spectrometer (ICP-OES). Silicon (Si) is typically present in petroleum liquids as soluble organic silicones, but the method will also detect other forms of silicon (Si) such as the generally insoluble inorganic silicon (Si) salts and silica. The method is primarily used to analyze reformer charge stocks for silicones, but may also be used for refinery charge stocks as heavy as vacuum gas oil (VGO). The lower limit of quantition is approximately 1.0 mg/kg (mass-ppm) as silicon (Si). Standard addition, as described in the Appendix, may be used to verify the results.