US National average right now for gas and diesel is:

$3.13 regular
$3.55 diesel

That's a difference of 42 cents or about 12%. Considering diesels get anywhere from 20% to 40% better mileage than a comparable gas engine, a diesel is still making out pretty well, even with diesel fuel prices at their winter peak.

The problem though, is that we don't have too many comparable engines anymore. The diesels in 3/4 ton and 1 ton trucks have become performance options instead of money saving options, thanks to a hp/tq war between truck manufacturers.

From what I've been reading though, that should change very soon. As, a lot of manufacturers have smaller and less expensive diesels coming out. Closer to what we see in Europe.

I would love a Jeep Unlimited 4-dr in deisel. It would be perfect in my mind.

That seems to be a similar story to Diesel prices in the UK. Wierd when you get better fuel mileage from it, it requires less processing by the refiners and with the new particulate filters can be as clean as a traditional Petrol engine at the tailpipe.

If anyone is considering a new hybrid and are happy to wait you might want to hold off a few months to see the details of the new Prius (due on roads 2009) and a new version of the Honda hybrid that is in the works, plus a number from other makers that are supposed to be significantly more efficient.

I would be interested if anyone can comment authoritatively on the economics of diesel fuel: I have heard from one source that diesel fuel is distinct from gasoline, in that diesel is a petroleum middle distillate and comes out of a refinery separate from gasoline (and kerosene etc). So that if the US vehicle fleet as a whole were to switch from gasoline to diesel in order to take advantage of diesel's benefits, its not so much a matter of switching over production of gasoline to diesel to meet the higher demand (because you can only get x amount of diesel from y barrels of petroleum), its a matter of importing more petroleum to make more diesel, and possibly raising prices for an ever scarcer diesel fuel. In other words, the US is still in global competition with other consumers for that barrel of oil, whether that barrel yields diesel or gasoline or both.

Disclaimer: I own three gas-consuming cars and I swear I'm not at the sharp end of some anti-diesel community, I would like an answer to the question though: if the US were to see a 20, or 50% increase in diesel demand from autos, what happens to petroleum demand (from which gas and diesel are made), and what happens to diesel prices, to answer the demand?

IANAPE (I am not a petrochemical engineer ) but I believe that the statement is correct but doesn't tell the whole story. As far as the actual distillation process is concerned, there is a fixed amount of diesel in each barrel of crude. However, after that step, there are additional chemical processing stages that can convert one product into another. I know that refiners do this for gasoline to increase the yield of gasoline from each barrel beyond the fixed percentage you'd get just from straight distillation, so I don't see why it wouldn't work with diesel as well. However, you'd probably have to spend a lot of time and money building new processing facilities to handle a 50% spike in diesel demand if so many people switched over.

Something to consider in that equation. There's millions of gallons of used restaurant cooking oil going to waste every day that could easily be converted to biodiesel. I wonder how much that would affect diesel prices. Right now, restaurants have to pay substantial amounts for grease collection. I'm sure they'd be more than happy for someone to take their "waste" for free. Although they might see it as a way to make money and start charging for it.

The "french frymobiles" as they are lovingly called are a good option. The hurdle has to do with some of the regulations dealing with "disposing" of the waste. Basically, if a union-controlled company can't "properly" dispose of it then it will be blocked for average Joe to get his hands on it in bulk. In general I have no problem with the restaurants making a few bucks off of selling their old oil. It is a legitimate commodity and there would be a legitimate market for it.

Remember, when Deisel invented his engine it was designed to run on vegetable oil. Ditto for Ford and his engine.

My parents ran a small restaurant for several decades. They said that when they started, companies would pay them to pick up their used oil. Not sure when things changed and then they had to start paying to have it hauled away.

I'd check with your state government before fueling solely on biodiesel. I've heard of more than a few cases where somebody makes their own fuel, the government finds out, and the next thing they know they get HUGE bill for tax on the manufacture of fuel. In one case it was a guy in his 70s getting a bill for over 7000 dollars all at once.

Its not a tax on the manufacture of it, its a tax on using it on the road. The gas station pump price has the road tax added in so when you make your own your not paying that tax. They only tax if your driving on the road, for example my parents buy diesel for their farm tractors and they tell the gas station ahead of time and don't have to pay the road tax.

I'm trying to find a way to go straight from crop to biodiesel, everything I find on it tells how to convert from vegetable oil so I'd have to make vegetable oil then convert to biodiesel, I'm wondering if there is a more direct method.