I don't claim to have originated the idea myself, and in truth am not even sure where I saw it first - most likely The Oil Drum.

Whatever the first source, it's still a good idea. As usual, though, the devil's in the details... The illegal immigrant issue you mentioned for one, and the diesel/trucker issue that someone else has brought up. There's a real argument that the same tax should be applied to truck diesel, because that's a really energy-inefficient way to transport freight and we'd like to cut it back. OTOH, neither do we want to bankrupt every OTR driver overnight. Perhaps a phased-in solution would be best, to allow that segment to adjust; it'd be really good if we could rehabilitate freight rail in the US.

But yes, absolutely diesel needs the same high tax. What about biodiesel? Well, here's a hybrid idea: Base the tax on the carbon footprint of the fuel, so it's more like a carbon tax. So pure fossil fuels are highest, ethanol with a poor EROI is second, and good biodiesel is significantly lower. If a truly green fuel was developed (hydrogen from renewable electricity maybe), it would have zero tax under this plan. But then, what about electric cars? Sure they're more efficient generally, so we'd like to encourage them, but if they're being "fueled" by non-renewable power, they should still share some of the burden. The further we take this kind of discussion, the closer we get to a generalized carbon tax, just offset by rebates or credits.

Moving on, the issue about the working poor who need to commute long distances is another thorny one. Frequently, this is a case of semi-affluent areas employing people who can't afford to live there, and there would certainly be something more honest (and less exploitative) about reducing that disparity. But again, many of the people who would be really hurt are the ones who are just scraping by, who are working in a better neighborhood or wealthier town because there isn't enough employment where they can afford to live. Perhaps that could be offset by the spending of the tax rebates? After all, people with lower incomes are more likely to spend their rebates (rather than invest them), and with a hefty gas tax they'd be more likely to spend them close to home.