Let's imagine that when gasoline prices increase by 50%, gasoline purchases decrease by 25%. Using the formula above, we can calculate that the price elasticity of gasoline is: Price elasticity = (-25%) / (50%) = -0.50 Therefore, we can say that for every percentage point increase in the price of gasoline petrol, the quantity of petrol purchased decreases by half a percentage point. Price elasticity is usually negative, as shown in the example above. This means that it follows the law of demand; as the price increases, the quantity demanded decreases. As the price of gasoline increases, the quantity of gasoline demanded will decrease. Positive price elasticity is rare. An example of a good with positive price elasticity is caviar. Caviar buyers are generally wealthy individuals who believe that the more expensive the caviar, the better it must be. Therefore, as the price of caviar increases, the amount of caviar demanded by wealthy people also increases.