Diesel fuel is not usually more expensive than gasoline (petrol). On average diesel tends to be slightly cheaper although the prices do sometimes cross-over at times because the prices are linked to crude oil, taxes, local supply demands and production/refining capacities, which constantly fluctuate.
While Diesel has a higher energy density and energy content which gives it better MPG for diesel engines, gasoline, however, tend to contain additives and taxes/fuel duties levied in many countries which can cause it to come at a lower average price at times.
