Again: Show your math. How do you figure out what the "externality" is? What's to stop you from saying it's $500 per barrel of oil consumed if that would result in your desired policy outcome?
I'm not advocating a specific policy. That's up to economists to decide. Here's the conversion as I see it:
embro: I wish gas was more expensive
pearkes: People in rural areas are very dependent on cars and would be disproportionately affected by increased gas prices
me: Cars have a lot of associated externalities such as CO2 emissions and air pollution, taxation is one way to internalize these externalities. If this process disproportionately affects rural people, it's because society has been subsidizing them by accepting the effects of their externalities. If this results in higher corn prices, for example, then corn prices should be higher to reflect it's true cost to society. By giving the market the true prices of goods it can more efficiently allocate resources.