An application of electrospray ionization/mass spectrometry for identification of various commercially refined fuels using the unique signature of polar components, was investigated. The samples were analyzed by mass spectrometry using negative electrospray on an Agilent Series 1100 liquid chromatograph/mass spectrometer. These analysis were applied to hydrocarbon samples from a large, long-term fuel spill which were taken from the subsurface and different extent of biodegradation or weathering. The technique provided rapid identification of hydrocarbons released into the environment because these polar compounds are unique in different fuels.