The popular RON 95 variety and biofuel E5 RON 92 have become 3.6 percent cheaper at VND28,150 and VND27,300.
But the prices of kerosene, diesel and mazut were adjusted upward by 2.4-6.4 percent.
Gasoline retail price adjustments, if any, are usually made at 3 p.m on the 1st, 11th and 21st days of each month, but this time it was made at midnight on the 31st as the environmental tax cut became effective.
The tax, the biggest of all taxes and fees on fuel, has been halved to VND2,000 on gasoline, and cut by VND700-1,000 on other fuels. They will remain in force through this year.
Without the tax cut, gasoline prices would have risen by VND1,000-2,800 per liter on Friday.
On the global market, the price of crude oil has dropped to $100 per barrel at the time of writing from last week's average of $114.