For C02 yes, diseasels are cleaner... and monoxide. But, diesels have far more particle emissions which are indecently harmful. The newest of the diesels... usually from the VAG group, with the HUGE catalytic converters are cleaner, yes, but 75% of diesels are dirtier and more harmful to human, animal and plant life than any equivelant petrol. (Obviously a Veyron is going to be more harmful!!) ← However... Diesel cars are better than petrol cars with reference to carbon dioxide, the global warming gas. Diesel cars are better than petrol cars with reference to carbon monoxide, a poison. Diesel cars are better than petrol cars with reference to hydrocarbons which cause cancer. Diesel cars are similar to petrol cars with reference to nitrous oxides, which cause smog. Diesel cars are worse than petrol cars with reference to particulates, which have unproved health impacts.