Richard Aucock:

In the UK of the 1980s, diesel drivers were outcasts. They were required to fill up around the back of the station, over by the truckers, to be looked upon by gasoline burners with a mixture of pity and smugness. And that presumed diesel drivers could even find somewhere to fill up, as not every filling station bothered to stock their fuel.
 This sheer lack of availability led to great variability in pricing. As the only filling-station proprietor in 25 miles to stock diesel, Mr. Smith could subsequently charge more or less whatever he wanted. A survey of diesel prices in the US illustrates a similarly maddening snapshot of how scarcity can produce wide price fluctuations, with pump prices varying by up to 50 cents a gallon. But with more diesel purchasers, the laws of the marketplace would kick in, bringing prices into greater alignment.
 Given the need for low-sulphur refining, diesel would not necessarily become cheaper than premium in the US. It is pricier on the other side of the Pond, too, but although Europeans gripe about it, they still know the savings add up. Diesel generally returns 30% better mileage than gas, and in the dominion of $8 gallons, this is no small advantage.
 Mind you, there are two distinct factors working in favour of Europeans’ wallets: fuel with a higher cetane rating, which makes it easier to control NOx emissions, and EU emissions standards that are generally comparable to the US’s Tier 2 standards in all areas apart from, yes, NOx. Even our EU 6 standards, due in 2015, do not quite match the States’ strict limits on smog- and acid rain-causing emissions.