More aid will be announced, the government said, but critics said homes now need more security.
Most oil-dependent households put money aside themselves or with a supplier to build up cash for when oil is needed, to spread the cost over the year.
But the Countryside Alliance, which represents rural homeowners, many of whom depend on heating oil, said the rapid rise in oil prices “will have left many without enough money to fill tanks and not enough time to make up the shortfall”.
According to comparison site Boiler Juice, home heating oil prices shot up from an average of 62 cents per liter to over £1.50 in March this year.
Homeowners who are not connected traditionally buy oil towards the end of the summer, when prices are much lower. But according to Boiler Juice, the oil price only fell to 86 pence per liter in August, which is still a 348 percent increase compared to April 2020.
The Countryside Alliance said low- or fixed-income households will find the coming winter “particularly difficult”.
James Legge, of the group, said: “£100 at current prices is a drop in the ocean. Most tanks hold over 1000 litres. The minimum supply is 500 liters and payments are made in advance – a supply of 500 liters is currently not far from £500.”
According to Certas Energy, an oil supplier, the average home uses 1,700-1,800 liters of oil annually, which would cost £1,500 at current prices, although some households pay much more.
Last month, The Telegraph reported that MPs living in rural areas declared more than £2,000 worth of oil supplies last year.
According to data published by TNZT Parliamentary Standards Authority, former health secretary Matt Hancock spent £2,751 on oil deliveries, while the ceiling on estimated annual household energy bills was below £1,200.
Nick Gibb, MP for Bognor Regis and Littlehampton, also claimed over £1,000 for heating oil.
Rural homeowners will still benefit from the £400 energy discount announced by Rishi Sunak in May when he was chancellor. This is automatically deducted from their electricity bill.
However, the Countryside Alliance said households would have preferred the £400 to go to oil, “which would allow at least 1 500-litre supply with the £100”.
Mr Legge said: “The government should also think about working with oil companies to fill tanks and then pay them off over a number of months. The abolition of VAT would also help, as with all energy bills.”
The Department for Business, Energy and Industrial Strategy was contacted for comment.