Young soft shell clams, Mya arenaria, were exposed to subacute concentrations of No. 2 fuel oil-in-water emulsions under simulated winter (4 C) spill conditions. A pattern of accumulation and discharge of petroleum constituents, an experimental depuration time (biological half life, TB50), and a potential transport mechanism of aromatic compounds from the fuel oil to the clams were experimentally determined. The clams were exposed to single dose concentrations of 10, 50, and 100 ppm of No. 2 fuel oil-in-water emulsions for 28 days. Clams accumulated the greatest amount of hydrocarbons within one week of the initial exposure. The accumulated hydrocarbons decreased each week as the hydrocarbon content of the water decreased. Mass spectrometric analysis determined that the principle compounds accumulated and retained after 3 weeks of oil exposure were monomethyl, dimethyl and trimethylnaphthalene isomers. Depletion of oil from the water column and accumulation and discharge of fuel oil constituents appeared to involve a mucus-oil complex formation by the clam. During the depuration period, accumulated hydrocarbons were rapidly, although incompletely, discharged. At the end of the depuration period, many of the hydrocarbons present in the clam were dimethyl and trimethylnaphthalene isomers. The biological half lifes calculated were: 10 ppm (50 days); 50 ppm (11 days); 100 ppm (13.5 days).