Answer:
Oil price
Explanation:
THe oil price effect states that when the oil price rises, most of the products that need oil to be produced or transported also will rise, and when oil price decreases most of the same products should also lower their prices, in this case gas is the one of the most related products to oil, since it is the main product of oil, and a decrease in the cost of oil will result in a direct decrease in the price of gas.