1 gallon of gasoline would charge 1 iPhone, once a day, for 20 years.

http://www.exxonmobilperspectives.co...rge-an-iphone/

Interestingly - as diesel has greater energy content than gasoline, it is underpriced in the US (i.e. not enough more expensive). However, E85 is overpriced.

In a real sense, the diesel underprice is offset by the ethanol subsidies.