The 180-cst fuel oil crack, which measures the price difference between the heavy distillate and Dubai crude on a per barrel basis, stood at minus $2.83 a barrel on Wednesday, versus $3.41 a barrel the day before.
The more negative the value, the bigger the loss for refiners producing fuel oil.
January 380-cst fuel oil swaps were traded at $261 a tonne, compared with $258.50 a tonne on Tuesday.
The rise in deal level was despite Dubai crude shaving 8 cents a barrel on Wednesday, or an equivalent of around 60 cents a tonne.
In the marine fuel segment, bunker tankers to deliver the ship's fuel were heard to be in tighter supply for delivery within three to five days.
As a result, asking prices for prompt delivery reached a premium of as high as $8 a tonne above oil lifted from tanks.
Comparatively, premiums for delivery up to 10 days forward were only around $2 a tonne, traders said.