There was once upon a time when diesel was the king of getting you somewhere cheap. Prices were lower, engines consumed less over long distances. The black smog of the diesel engine was the choice of the man chained to the carriageway. In the last twenty years, it seems that the difference between petrol and diesel engines has become a thin margin. Petrol always equalled performance. Diesel was equal to efficiency. Improvements in technology and price changes in the fuel market have virtually leveled the playing field. So, what was the difference, is the now difference and what does the future hold?