Hello

There are dozens of the E-class models each with differing fuel economy as the wheel size/transmission/engine size combination is very large...

However if you consider like for like... so a E250CGI vs E250CDI for an automatic 5 speed transmission on 17" wheels the diesel cdi returns a combined figure of approx 45mpg compared to 34mpg for the petrol CGI

The diesel is the more efficient model.

The new generation of directly injected petrol engines are no doubt closing the gap but the diesel is still better..

The following site is excellent for comparing all the fuel economy numbers

http://www.vcacarfueldata.org.uk/search/search.asp

Use the drop down menu and choose: Mercedes: E-Class and specify the All option and you will get all the models.

Once chosen the page comes up with the 'grams' format, but just click on the more info link and you get a whole lot more data....

Personally I would always go for the diesel option, but every now and again you should hit the motorway to stop any build up accumulating within the engine... this is really just a preventative measure and shouldnt really influence your decision...

If you need any more information just get back to me

All the best

Jon