Iran, the second largest crude producer among the Opec members, will introduce petrol rationing for motorists from Wednesday.
"From midnight tonight gasoline will be rationed," state television said on Tuesday quoting a statement from the oil ministry.
Despite its huge energy reserves, Iran lacks refining capacity and has to import about 40 per cent of its petrol needs, a sensitive issue when world powers have threatened fresh sanctions over a row with Tehran over its nuclear programme.
The imports are also a heavy burden on state coffers because all fuel, whether imported or domestically produced, is sold at heavily subsidised prices. Even after a 25 per cent price hike, fuel is still sold at just 1,000 rials [11US cents] a litre.
The announcement followed months of uncertainty about how and when rationing would be implemented. A major part of the debate between parliament and government has focused on whether drivers would be allowed to buy extra fuel at market prices.
Tuesday's announcement made no mention of that.
"The government, by being completely committed to implementing the law, will exert all its efforts to decrease any possible limitations for people," state television said.
It said private cars, which cannot also burn compressed natural gas, would get 100 litres of petrol per month. Some cars in Iran can burn both types of fuel and those vehicles would receive a smaller petrol ration, according to the state television.
For the time being, private drivers would be able to buy their daily allocation up to four months in advance, it said, adding that this period could later be extended to six months.
Official taxis which only consume petrol would get 800 litres per month, while other drivers who have part-time taxis will get 600 litres per month. Government cars will get 300 litres per month.
All petrol is already sold using electronic "smart" cards.