This method, also called hydrocarbon oil index (HOI), mineral oil, or total petroleum hydrocarbon (TPH) determination is one of the most important applications in environmental analysis because it represents the highest sample loads in many laboratories. The Hydrocarbon Oil Index (HOI) is defined as the total amount of compounds which can be extracted from the sample (potable water, surface water and waste water) with a non-polar solvent having a boiling point between 39°C and 69°C (replacing the use of halogenated solvents). NWTPH-HCID is a qualitative and semi-quantitative screen to determine the presence and type of petroleum products that may exist in water or soil. This method should be used if the type of petroleum contamination is unknown. For petroleum releases, these contaminants of concern are typically aromatic compounds like benzene, toluene, ethylbenzene and total xylenes (BTEX), and polynuclear aromatic hydrocarbons (PAHs) like naphthalene (N) and benzo (a)pyrene. Hydrocarbon numbers ranging from C15 to C50 are found in the various types of mineral oils, with the heavier distillates having higher percentages of the higher carbon number compounds (IARC 1984). Oil is made up of many types of hydrocarbons with various molecular structures and properties. TPH are a summation of the identifiable hydrocarbon compounds in the oil. Total Petroleum Hydrocarbons (TPH) refers to a vast group of organic compounds commonly found in crude oil and its various refined products, such as gasoline, diesel, and lubricating oils. There are many analytical methods used to quantify soil, sediment, and groundwater petroleum concentrations. This document discusses the most common and has tips on reporting your results. 3.3 Appropriate standards must be used (i.e., diesel standards for diesel analysis, JP-4 for analysis of JP-4, etc.), or excessive false negative or false positive rates may result. The system described here represents a valid option for the determination of the Hydrocarbon Oil Index in water. The solid chromatographic result, coupled with the brief GC runtime and the 155 autosampler positions, allows high productivity.