A scheme is described for gross and detailed chemical characterization of oily waters. Total, suspended, and dissolved organic content and hydrocarbon levels of the sample are determined. Volatile and water-soluble fractions are char acterized in greater detail. Lower aliphatic and aromatic hydrocarbons are separated from the water by nitrogen sparging and are collected in an activated carbon absorption column. They are then extracted into carbon disulfide and analyzed gas chromatographically.The water-soluble frac tion is extracted into chloroform or adsorbed on Amberlite XAD type of resin. Class characterization of this fraction is performed using the HPLC procedure. GC-MS-C is used for detailed analysis. The methodology was used for study ing the effectiveness of bilge and ballast water treatments.