For German car drivers, filling up the gasoline tank in September was the most expensive it has ever been in history. The monthly average for a liter of super was 1.37 euros, 5.8 percent more than the August price. Diesel, at 1.14 euros per liter, was 1.7 percent higher than in the previous month. Compared to a year earlier, super was 20 cents more expensive while diesel rose 18 cents. According to economists, the high prices can be traced back to higher purchasing prices on the Rotterdam oil market, where the price for super rose 10 percent and for diesel, 5 percent. The price jump was also exacerbating by Hurricane Katrina in the United States, which caused serious damage to oil refineries and platforms in the Gulf of Mexico region.