More on diesel
I'm not a math whiz, but the higher price of diesel, is clearly counteracting the financial benefits of the increased fuel economy.
That is true. As cowboyind points out, this is a temporary thing. Diesel prices always go up when it gets colder because there is so much more demand for it: cars, trucks, and locomotives use more fuel when it's cold out; home heating oil is essentially diesel; and even airlines use more because people are traveling for the North American winter holidays (Canadian Thanksgiving is pushing "winter" a little bit, but U.S. Thanksgiving and Christmas certainly meet the test). But this price trend is not at all typical. And, though I'm not much of a conspiracy theorist, it would not surprise me in the least if people in the White House called a few of their buddies in the business and asked them to refine more gasoline to drive down the price and keep us proles quiet.
Someone in another forum on another site did the math and figured that, at today's unleaded and diesel prices, a gasoline-fueled car getting 38 mpg highway would cost the same to run as a diesel getting around 50 mpg highway. But that is now. With the price of diesel the same as that of unleaded, the 50% better mileage I get on my diesel compared to a gasoline-engine VW provides a relatively quick payback.