Currently, diesel prices in the U.S. are slightly higher than gasoline. Across the pond, the story has been somewhat different. With the exception of the UK, diesel in Europe has usually been cheaper than gasoline. This was a consequence of European governments' policies on taxing fuels. Trucks and buses run on diesel, whereas cars traditionally ran on gasoline.
Nevertheless, producing diesel is more expensive than producing gasoline. For instance, according to the Spanish Ministry of Energy report on fuel prices, a metric ton of diesel cost about $826 compared to $803 for unleaded during the past month of January.
What Europeans pay at the pump differs a lot depending on the country, and not only because of taxes. Cost price of gasoline is from 47 euro cents/liter in Sweden to 60 euro cents/liter in the Netherlands. The average EU price is about 53 euro cents/liter. In the case of diesel, prices start at 51.7 euro cents/liter in Bulgaria and top 64.2 cents in Italy; the average for the EU is about 60 cents/liter.
Now let's add taxes. The most expensive gasoline in Europe last January was on sale in the Netherlands. The Dutch paid an average of 1.506 EUR/liter compared to 0.917 EUR/liter in Bulgaria. The average was 1.328 EUR/liter. In the case of diesel, Britons paid the most: 1.463 EUR/liter whereas Bulgarians paid 0.924. The average price of diesel in the EU was 1.234 EUR/liter, still cheaper than gasoline but in 14 out of 27 countries, diesel was more expensive than gasoline in January. The signs point toward a continuation of this trend. Spain's diesel became more expensive than gasoline in March, and both France and Italy seem likely to achieve the same price in the near future.
[Source: Spanish Ministry of Energy]