This scenario works when prices are going down. When the replacement cost is going up it can bankrupt a ma and pa business. Example, 10,000 gallons bought at $1/gal (easy math). The profit margin on fuels for these types of operation is 3-4% Gas stations make their money by selling Monster Drinks, pizza and cigarettes. Sell 10,000 gallons, at 4%, the gross is $10,400. When the cost of gas goes up to $1.25, the replacement inventory costs $12,500. Where does the $2100 come from?
There are replacement cost formulas to keep ma and pa solvent, but when the swings are wilder, as we saw with the recent Iran panic, ma and pa often don't survive.
Crude market "panic swings" are all driven by speculators. Refineries operate on long term supply contracts and fill shortfalls in production due to increased demand by purchasing on spot markets. Speculators never touch a drop of oil, they just shuffle paper and the consumer pays.