To effectively determine the fate of spilled oil in the environment and to successfully identify the source(s) of spilled oil and petroleum products is extremely important in many oil-related environmental studies and liability cases. This article briefly reviews the most recent developments and advances of the gas chromatography-based technologies that are most frequently used in oil-spill characterization and identification studies. The effects of oil weathering on the chemical composition features and changes of spilled oils in the environment are also addressed. The fingerprinting and data interpretation techniques discussed include recognition of distribution patterns of petroleum hydrocarbons, oil type screening and differentiation, analysis of "source-specific marker" compounds, determination of diagnostic ratios of specific oil constituents, and application of various statistical and numerical analysis tools.