Hiya, just started a new job that involves a 54 mile commute covbering the M55, M6, M61 and M60 every day, its a joy!! As I start at 7am its not too bad to be honest. Anyway, tried the journey on Optimax and got 39 - 40 mpg, same journey on cooking unleaded and got 36 mpg!! The maths gives: Fuel Type: ((Mileage per month/MPG)*litres per gallon)*cost of fuel = monthly cost. So, Optimax: ((1500/39)*4.5)*0.94 = £162.69 Normal: ((1500/36)*4.5)*0.89 = £166.88 So, it might be more expensive up front, but its cheaper in the long run. This trip carried out at the same times, very similar conditions and with only me in the car travelling at very similar speeds. Diesel would be cheaper, but not by much: Diesel: ((1500/50)*4.5)*0.95 = £128.25. This is a saving of £38.63 over normal and £34.44 over optimax, a saving of £463.56 per year. Yes it would be chaper to run the diesel, but, would cost me more than £500 to sell my car and buy a similar reg'd car with similar spec and mileage.