THE point came when I thought the trip computer had fried its chips.
There it was in black and white - 955 miles to empty, and I had already driven for 45 minutes on the M6.
Okay, so I was travelling at an optimum 50mph through one of those frustrating average speed checks, but it shouts volumes for the car that such a number could even register.
Especially when the vehicle in question is an executive saloon weighing 1.6 tons and housing, would you believe, a 1.6-litre engine.
But then the Volvo S80 DRIVe model is a luxury car with a big difference - it's not only the most economical version of the S80, but also the cheapest.
It comes as part of the Swedish manufacturer's eco assault, spearheaded by the company's DRIVe range with dramatically reduced CO2 levels and improved fuel efficiency.
And the Swedes have been able to force the emissions way down without having to compromise style, safety or driving, and in some cases still retain the option of a sporty R-Design package.
The million dollar question of course is whether such a small engine can offer much in the way of performance when dropped into a car the size of an S80.
Let's be honest, it's not the most spirited of units away from the lights, but as soon as the car picks its feet up the response is excellent.
There's plenty of mid-range pulling power to go with a supple ride, premium soundproofing and a positive feel from the steering.
This model also included Volvo's blind spot warning system, whereby orange lights flash if another vehicle is advancing on either side of you - something more car makers should adopt.
All models with the DRIVe badge have a lowered chassis - which helps reduce fuel consumption - front airflow deflectors and a lower lip spoiler plus low rolling resistance tyres.
Improvements have also been made to the engine and gearbox management software, so there's electro-hydraulic steering and a Gear Shift Indicator to tell the driver the best point to change up or down.
The combined effect is substantial and after clocking up nearly 500 miles the onboard computer revealed an average of 57.2mpg, fractionally less than the official figure of 57.7.
It was all achieved in leather-clad comfort with ample interior space and a large, long boot.
In fact the only criticism of the cabin is that it's too drab and minimalistic for my taste - predominantly black plastic with hints of metal.
Volvo has this month revealed a 119g/km version of the S80 DRIVe - with a fuel economy boost that increases the car's range to nearly 1,100 miles. Its lower excise duty band means owners will pay just £35 a year.
FAST FACTS
Volvo S80 1.6D DRIVe SE saloon
Price: £23,245
Mechanical: 109ps, 1,560c, 4cyl diesel engine driving front wheels via 5-speed manual gearbox
Max speed: 118mph
0-62mph: 12.4 seconds
Combined mpg: 57.7
Insurance group: 10
CO2 emissions: 129g/km
BiK rating: 18%
Warranty: 3yrs/ 60,000 miles