There are many benefits of a Euro 6 standard diesel engine … Increased Efficiency -As manufacturers have to make sure engines are as efficient as possible to meet standards they provide the added bonus of producing increasingly fuel efficient engines and so increasingly cost efficient engines. On average a diesel engine will have up to 30% better fuel economy compared to a similar petrol engine. Reduced CO2 -On average a diesel engine will produce up to 25% less CO2 than a petrol version so companies can reduce their carbon footprint. As road tax is currently calculated by CO2 emissions a diesel engine could be more cost effective. Future Proofing – Diesel engines have been getting bad press lately, but a distinction is made between old diesel engines and new diesel engines. The future of older diesel engines is unclear but is likely to include extra costs to discourage use. For example London Mayor Sadiq Khan would like to charge older diesel engines an extra £10 to drive in the capital on top of the usual congestion zone.