While the amount of oil in water is highly regulated, it can also be a challenging measurement. It is complicated by the fact that oil conies in many forms and the measurement is defined by the particular regulatory method. When EPA 1664 is the regulatory method, the 'oil' is anything that is extracted into hexane and remains after the hcxanc has been evaporated and appears as weight. In regions where infrared analysis is the defining method, the 'oil' is whatever is extracted into the solvent and lias carbon-hydrogen bonds that absorb infrared light at a specific frequency. Each method reviews different properties of oil and can potentially yeild different results. Therefore, the answer to the commonly asked question of how one type of oil in water measurement compares with different regulatory methods is not always simple arid straightforward, listed below are four factors that need to be considered.