The techniques available for chemical analysis of pollutants are continually evolving. Concentrations of the potentially toxic components of oil can now be measured down to levels of parts per trillion (ppt, ng/kg, 1 x 10–12). One of the most important objectives of damage assessment studies is to establish both a pathway for the observed damage and the qualitative identification of the particular oil contaminant responsible, particularly in chronically polluted environments. This is usually done by Gas Chromatography linked to Mass Spectrometry (GC-MS) analysis.