It is a social media induced problem. Now the main stream media is covering it so it will only get worse. Most people fill up once a week. When everyone shows up the same day the store runs out of fuel. Add in all the extra vehicles of evacuees and holiday travelers, someone panics and starts posting, and so everyone runs to fill up the vehicle and gas cans.
Latest EIA report shows 230 million barrels of gasoline in storage so it is not a supply issue, it is a distribution issue. Most convenience stores only have 2 10,000 gallon tanks, 1 for 87 octane no lead and one for 93 octane no lead. The mid grade is blended by the pump. They would also have a tank for diesel if they sell it. When you have a run on fuel it doesn't take long to empty the tanks. The tanker coming in carries 8,000 gallons so it can go pretty fast. There are only so many tankers so it is tough keeping everyone supplied.
It will work itself out before long but we will all pay the price at the pump.