Gas prices in just the last ten years have rocketed by three dollars. It took six years to double to two dollars. Four years later, gas prices doubled once again to four dollars a gallon. The dramatic increase in price of oil has been the biggest factor of gasoline price increase. The increase is also just simply a supply and demand case. The increase of the supply of oil has not kept up with the supply of demand of the oil so the prices go up.
The United States uses one fourth of the world's oil even though it's less than 5% of the world's population. Gas prices can go up not just based on the prices of oil. It can go up from the cost to make oil into gas, the transportation costs, and the profit the gasoline dealer has. It's predicted that the price will become $6 or $7 very soon.