Adult specimens of Crassostrea rhizophorae were exposed to diesel oil dispersed in seawater. The experiment consisted of a 10 days contamination period and 15 days depuration period. Oyster samples were extracted, and analysed by gas chromatography and UV fluorescence spectroscopy. The concentrations of n-alkanes, branched alkanes, unresolved complex mixture (UCM) and aromatic hydrocarbons were determined. The oysters accumulated the hydrocarbons rapidly, reaching a maximum concentration of 387.5 ug/g (wet weight). After exposure to uncontaminated seawater, the oysters were able to reduce their hydrocarbon load to 5.6 ug/g. The data indicates that C. rhizophorae is capable of preferential accumulation and depuration of hydrocarbons. Apparently, the oysters are capable of modifying the straight chain alkanes and branched alkanes to yield a mixture of components eluting as UCM.