content: I don't see how much more efficient you can get with petrol/diesel engines. I mean, thermodynamically they're gonna top out at 30-40% no matter what you do, and the drivetrain in a modern car is 80-90% efficient, so there's not a lot more improvement to be made on the overall fuel-to-wheels energy efficiency front. All that's left is cutting off corner cases (such as hybrid cars removing the need to run the engine during stop-start traffic) and reducing the total amount of energy required. You're not going to get a car with nice interior, stereo, aircon, good luggage space, EPA-compliant emissions, a 5-star ANCAP rating, nice grippy tyres... AND it be so light and easy-rolling that it gets amazing fuel economy. It's all a giant pile of tradeoffs.