Something missing in ‘economics 101’

As I recall, the price of gasoline slowly began to rise way back in the early 1970s. The perceived problem: supply and demand. Quantities (supply) were said to be limited and demand was increasing, so that increased upward pressure on prices. A few years later, motorists were forced to buy gasoline on either even or odd numbered days. Some stations in the West even limited the number of gallons that one could purchase. The perceived problem: supply and demand. Today, motorists can buy as much gasoline as they want, as long as they can meet the price. Hmm, what am I missing here?