Back in 2007, I did an analysis of the then-new BMW 5-Series sedan, which showed the class-leading efficiency of its 6-cylinder gasoline engines. It can be seen in full here. This showed the significant lead that BMW enjoyed over many of its competitors. Over three years on, I’ve just repeated the analysis of fuel efficiency in automatic transmission E-Segment sedans, which also include the Mercedes E-Class and Audi A6. To compare apples-with-apples, only models on sale in Europe, and thus with a European drive cycle fuel economy figure published, were looked at. The results were perhaps surprising. Gasoline powered models have seen a very modest increase in efficiency, but have seen outputs rise more sharply. The overall unweighted average fuel economy of the models surveyed improved by around 5% from 10.1 to 9.6 l/100km, while power output rose by over 13% from 193 to 219 kW. The story for diesel was somewhat different: the overall average economy of the models surveyed rose improved by over 15%, from 7.3 to 6.2 l/100km. Power outputs were up by less than 8%, from 140 to 150 kW. This is arguably because manufacturers have focused their economy efforts on the models which buyers who care about economy purchase – which are typically the diesels. Gasoline models are more popular in non-European markets, such as the USA, where fuel is cheaper, and where E-Segment sedan buyers have traditionally been far less concerned with fuel economy than performance. My prediction will be that the next 3-4 years will see significant increases in overall gasoline engine efficiency in this segment, with many more 4-cylinder DI forced induction units being used, along with a much wider penetration of stop-start. This will be to meet the demand of those buyers in Europe in this segment who still choose gasoline - but also as a recognition that fuel economy is now firmly on the agenda in the USA and Asia, even for luxury sedan buyers. There's still room for improvement.