Well actually - especially in times of perceived or real crisis - gas panics are often the cause of gas shortages and price hikes, as opposed to the results of.

People freak out. Sense a shortage is looming. Or that prices will skyrocket. They never let their tank get less than half full. They head straight to the gas station to fill up. They come back to the pumps twice as often as they otherwise would. En masse. And so gas does end up running out. Supplies do end up running low. And the perception a shortage exists is further enforced.

So yes, most people buy gas when they're gettin' close to empty. That's when they need it. But at times like this people often end up thinking they need it more than they do and never let their tanks drop below 1/2 and so are toppin' off when they could afford to go a few more days and a couple hundred miles more without swingin' by the station.