Traders quoted 380-cst prices as low as $164 a tonne, from values on Wednesday of $167/$169.
They said 180-cst was offered around $172 a tonne, down from $176 a day ago.
Fresh government data showing higher onshore stocks of residual fuels was also pressuring prices, with most of the impact felt on 380-cst supplies.
Inventory levels rose 245,000 barrels in the week ended Wednesday to 10.675 million barrels, a level 24.5 percent above inventories reported in the same week last year, according to International Enterprise.
Marine gas oil was also down $1.00 from Wednesday to $294/$296 a tonne, traders said.