I was rather startled to hear a manager from another car company say his car of the show was the new S-Class.
After a brief moment of panic – how did I miss a new S-Class? – I realised he meant the new S250 CDI.
On the surface, this was one of the dullest cars around, but the point was that it is a big luxury saloon that can do over 40 mpg and emits just 149 g/km of CO2. It is also the first four-cylinder S-Class in the 60 year history of the model.
"So what?" you may ask. The point is that nothing is off-limits now. Car companies will look at any technology that makes their cars more efficient.
Audi has a concept powered by a rotary range extender, 30 years after the company's NSU subsidiary gave up on rotary engines.
Jaguar has a concept powered by a gas turbine, decades after gas turbines were written off for cars – too expensive, too much lag, too thirsty.
Now car companies are re-examining everything (although we haven't seen a steam-powered concept yet, thank goodness).
Mercedes has decided that, if a four-cylinder engine is the most efficient solution, buyers will jolly well have to get used to it.
The air at Paris was business-like – the car manufacturers were saying that after years of promises, it was time to deliver. Numerous manufacturers had production-ready electric cars and range-extender hybrids that will hit the streets in the next year or two.
Even Land Rover, the hate figure of green activists, showed its new Evoque with a CO2 figure of 130 g/km – that is less than half the output of last year's Range Rover.
Even Lamborghini has got the bug, with a new model that weighs just 999 kg in order to improve efficiency.
Petrolheads used to worry that all this green hand-wringing would lead us to drive modern-day 2CVs limited to a top speed of 70 mph.
In fact, CO2 limits are driving possibly the most fertile time there has ever been for innovation.
Take the Ford Focus ST, previewed at the show. It has a smaller engine than the last model (2.0 rather than 2.5 litres), so will be lighter and should be more agile. It is 20% more economical.
Oh, and it's 10% more powerful at 250bhp.
Better handling, better economy, better performance. What's not to like about the current efficiency drive?
And our star of the show? The Jaguar C-X75. Beautiful to look at, a top speed of 204 mph and featuring micro-turbine range- extenders giving next-to no emissions.
That leaves no box left unticked.