I'm still getting used to my 2010 diesel automatic, which means watching the fuel computer rather more closely than I would otherwise. I've owned more than 50 motors but this is my first diesel. When I bought the car I asked the Honda dealer whether I should use a particular brand of diesel and he said no. Since then I've done 7000km, mostly on diesel from my local supermarket (they have the market in France, rather than branded filling stations and I've never had any trouble with any of their petrol - unlike supermarket petrol in the UK). Fuel consumption has been very acceptable but I find the engine noisy and rough between 1500-2000 RPM. I had heard this could be a problem but my car shows no outstanding recalls for re-mapping according to Honda Europe. Anyway, I did a long trip over the last few days and after a couple of hundred kms I filled the car with diesel from the Super U supermarket, because I was passing it. What a transformation! The engine is quieter, smoother AND consumption has nosedived by the equivalent of about 6mpg. I noticed on the pump nozzle there was something about 'diesel with additive' but I didn't take any notice at the time. Since then I've filled at Super U twice more and the good news continues. So, can a different brand of diesel make such a huge difference to a particular engine? And, so I don't have to keep finding Super Us, can I buy this 'additive' stuff and put it in myself?