The government rations the amount of gasoline that consumers can purchase. A consumer who would have purchased more than the rationed amount of gasoline will instead purchase more gasoline over other goods. If the government starts to ration on its on the amount of gas a person can purchase, they will probably start to purchase more to make sure they don't run out. When not purchasing is soley up to a consumer, it's easier to spend less, but when it's controlled by the government people are more adapt to spend for fear of running out.