I'll go on record stating that I LOVE diesels, and I've owned a BUNCH of them over the years.
BUT......
According to the
EIA , diesel is $0.45 per gallon more than gasoline here in the US ($3.91 vs $3.56).
So, if you have a 2011 Volkswagen Jetta SE 2.5 automatic getting 33 mpg (official EPA freeway rating) using $3.56 gasoline it costs you $1723 to drive 15,000 miles. If you had 2011 Volkswagen Jetta TDI diesel auto getting 42 mpg (official EPA freeway rating) using $3.91 diesel it costs you $1396 to drive the same 15,000 miles. So you save $327 per 15,000 miles.
But you also paid a $2,300 premium for the diesel over a similarly equipped gas engined Jetta (GL w/ Convenience Pkg = $20,660 is the same car as $22,995 base TDI, except motor). That $2300 premium would take 105,000 miles to break even.
Let's make it more interesting and look at a 2011 Hyundai Elantra automatic getting 40 mpg (official EPA freeway rating) using $3.56 gasoline it costs you $1335 to drive 15,000 miles The Elantra and the Jetta are very similar in size, and they have the same horsepower (but the diesel makes more torque). They share similar 0-60 times. But it's cheaper to buy a similar Elantra, even with leather and moonroof and other additional features of a Limited, it is still $2300 less than a base TDI.
Maybe Americans CAN do math