"This should stimulate exports a bit. Fuel oil has been really weak the past year so they had to do something," a fuel oil dealer said.
Russia used to set refined products export duty at 90 percent of the crude oil duty, but abandoned that link last summer when it began to hike crude tariffs in line with booming market prices for its Urals mainstay oil grade.
Russia's crude export duty currently stands at $83 a tonne, while Urals was traded at around $40.35 a barrel, or $295 a tonne in the Mediterranean on Friday.
"The main principle is not to increase the tariff burden above what it would have been under the 90-percent system," Alexander Sakovich, deputy head of the finance ministry's customs department, told Reuters.
"The burden on producers has not changed if you look at the basket of refined products produced by the typical refinery."
Most Russian refineries produce around the same amount of light or medium products and heavy oils such as fuel oil. The overall average export duty burden for such a refinery remains around $51 a tonne.
But the changes may have a harsher effect on refineries that have undergone upgrades to boost the output of lucrative light products, such as Sibneft's Omsk plant.
Russia exports more than 100 million tonnes a year of refined products to international markets, almost half of which consists of fuel oil. The 90-percent link meant one tariff for all products, regardless of their market price, but Moscow has moved to lower duties on fuel oil since last September to reflect fuel oil's lower market value.