How is this meaningful? This graph doesn’t account for inflation
The purple line is adjusted to constant 2011 prices, and the green lines are all adjusted to 2021 prices. So the green and purple lines don’t directly compare to each other, but you can still get some idea of scale.
The SPR holds mainly crude oil, so you can’t just open a gas station and start selling it. It has to be sent to a refinery first, and once that happens the product that comes out is fungible.
In short it would be logistically simpler to just buy gasoline on the market and subsidize it. The subsidy is only 20-30 cents / gal as well.