Daniel Thomas is a business reporter.
Every household in the UK will get a discount on their energy bill this autumn as part of a package of new measures to tackle soaring prices.
The Chancellor said that the poorer households would get a payment of 350 to help with the cost of living.
Millions could be left struggling if energy prices go up again in October.
Mr Sunak said he had offered a lot of support for the UK.
The windfall tax on oil and gas firms will partly fund the package of new measures.
It comes a day after Sue Gray's critical report into lockdown parties in Downing Street and follows intense pressure on the government to do more to help people with the cost of living crisis.
Mr Sunak said in the Commons that the government would offer more targeted help to the elderly and disabled.
Mr Sunak said that people are facing challenges with the cost of living and that is why he is stepping in with more support.
We have a responsibility to help those who are paying the highest price for high inflation. I want to support millions of the most vulnerable people in our society. I said we would stand by people.
The typical household energy bill is set to increase by 800 dollars in October, according to the UK energy regulator Ofgem. Bills rose by an average of 700 in April.
12 million households could be pushed into fuel poverty, where they are paying more than 10% of their household income on energy, according to Ofgem.
The inflation rate, the rate at which prices rise, is at a 40-year high as the prices of food, fuel and other goods also surge.
Mr Sunak said global forces were mostly to blame for rising inflation, including the war in Ukraine, recent lockdowns in China and the continuing impact of the Pandemic.
He said that the situation had evolved and become more serious and that households were being hit hard.
A plan to give everyone in England, Scotland and Wales 200 off their bills from October will not happen.
The sum will be doubled and not have to be paid back.
Eight million households on means-tested benefits will be paid directly into their bank accounts in two lump sums, one in July and the other in the autumn.
There will be separate one-off payments of 300 to pensioner households and 150 to individuals who are most vulnerable to rising prices.