Parr of Atlantic salmonSalmo salarwere exposed to two sublethal flow-through concentrations (averaging 0.2 and 1.0 mg/L) of Hibernia oil-water mixture for up to 40 d to determine relative importance of loss of feeding and food conversion for this juvenile life stage. Oiled parr showed reduced growth for 14 d before growth rates approached those of controls. There were also more weight-losing parr in oiled groups than in control groups. Reduction in growth coincided with reduced food conversion efficiency rather than reduced food intake. Food conversion efficiency was lowest for parr experiencing the higher oil exposure. Net efficiencies in both oiled groups returned to control levels within 2 to 3 weeks, although overall efficiencies in oiled groups lagged behind the control group. Liver glycogen levels were generally lower in oil-exposed parr, whereas liver protein content and the liver-somatic index were higher in parr exposed to the highest concentration of oil. Energy reserves were lower in pan that lost weight during the experiment in comparison with weight-gaining pan. Results suggest that medium-term (2 weeks to 1 month) exposure to low concentrations of oil may have transitory effects on Atlantic salmon parr, but that chronic oiling may impair growth and may influence the timing of length-dependent smoltification.