One favorite answer of the pro-gas-taxers is that consumers will be led, by the tax, to conserve scarce fuel. But conservation of resources is one of the major functions of the free price system. The market economy is continually being forced to choose: how much of product X or product Y, of resource X or Y, should be produced now, and how much should be “conserved” to be produced in the future? Not just of oil and gas, but of everything else: copper, iron, timber, etc.
In every area, this “conservation,” this decision on how to allocate production over time, takes place smoothly and harmoniously on the free market. The price of every resource and product is set on the market by the interaction of demand (ultimately consumer demand) and the relative scarcities of supply. If the supply of X, now and in the expected near future, falls, then the current price of X will rise. In this way, an expected future decline in supply is met right now with a rise in price, which will induce buyers to purchase less, and producers to mine or manufacture more of the product in response to the higher price. You don’t need a tax to accomplish the task of allocation and conversation.
In fact, a tax is a most clumsy way of meeting the problem. In the first place, since government knows very little and the market knows a lot, the government will not hit the proper target; indeed, since government’s coercion comes on top of market action, a tax is bound to “over conserve,” to reduce the production of a good below the optimum. And second, unlike a price rise accruing to producers, a tax provides no incentive for supply to increase or productivity to improve.