When a product is selling at higher prices, more people are motivated to supply it. If Saudi Arabia can mine oil for $2 a barrel, prices above that justify extracting it there. Oil in Britain’s North Sea costs $12 per barrel to obtain, so the prices would have to be higher before drillers in Britain start producing. Across the world, locations differ in their ease of accessing oil - until the prices motivate the suppliers, the oil stays in the ground. A supply curve graphs how much product suppliers will sell at a given price. As the price increases, so does the supply.