The GLE 500e is a plug-in hybrid, so the fuel economy you achieve depends entirely on how you use it. If you regularly drive very short distances - around town, for example - and you keep the car charged up by plugging it in, you could theoretically use barely any fuel at all. Sadly, the reality is you're likely to run the batteries down and rely on the engine on most journeys and, in those situations, fuel economy is barely any better than a normal petrol-powered car. So in short, you're very unlikely to match the official fuel economy figures.