Before we all switch over to the hydrogen-based economy and the fuel cell becomes the green powertrain of choice for the automotive industry, there will be plenty of debate about the best and most environmentally sound powertrain solutions. How does diesel stack up against the gasoline-electric hybrid and where is diesel share heading? Rob Golding takes a look at some of the issues facing the proponents of diesel as well as the arguments put forward by one of the diesel engine's biggest champions, PSA's Jean-Martin Folz.