Up here gas is 3.1 per gallon and diesel is 4.126. That's a 33% difference. As long as the difference is below 60% I'm better off driving my TDI than my Elantra.
I just checked in the US and you guys have a much higher gas/diesel price gap than up here. That might make the gasser less expensive at the moment.
But we're looking at the long term here. In fact I just went to
Energy Information Administration - EIA - Official Energy Statistics from the U.S. Government and extracted Weekly U.S. Regular Conventional Retail Gasoline Prices and Weekly U.S. No 2 Diesel Ultra Low Sulfur (0-15 ppm) Retail Prices since 2/5/2007 (since when ULSD prices are available) and compared both on a weekly basis. The average weekly price gap between the two is 11%. So, over the time ULSD has been here, it's been more economical to run a diesel than a gasser.