But common rail injection and major advances in under- bonnet electronics technology has allowed a total of 14 car manufacturers to market diesel models that are capable of eking out a gallon to more than 60 miles in the official UK combined cycle test.
The fact that major players including Ford, Vauxhall, Volkswagen and PSA Peugeot Citroen feature prominently in the line-up means cost-conscious fleet operators are already starting to factor in smaller cars when the time comes to replace urban fleets. But do the new-age economisers have the stamina for more ambitious work?
In a bid to find out if a runabout model can be practical in the long run, Fleet News has just packed 3,000 miles into a week behind the wheel of the most frugal car on sale in Europe.
With an official 68.9mpg to its credit, Citroen's C2 presents a persuasive case for itself as a trendy tiddler. Just as its designers intended, the car is perfect for use about town, where small overhangs, light steering and a tight turning circle make it child's play to thread through congested streets.
But with a diesel engine under its bonnet, the French shopping trolley reveals another side to its funky character – as a motorway express. It might sound incredible, but it's true: this car will pound along major routes with the best of them.
While the rest of the Fleet News team jetted to the Geneva Motor Show, yours truly used the diminutive Citroen to reach the Swiss event. And for good measure, the car was taken on a circuitous route that included crossing northern Spain.
How the C2 (pictured) stood up to extreme use such as this came as a pleasant shock for two reasons. Firstly, despite prolonged high-speed progress across autoroutes and scaling a few mountain passes into the bargain, the car managed to cover more than 60 miles for each gallon of diesel it consumed, most of them at average speeds of more than 70mph.
Yet it was the way it tackled the test that made the case for going 'eco' even stronger. Though its HDi engine is not the most powerful 1.4-litre version made by PSA, it feels remarkably potent in this application because it is pulling relatively light bodywork.
With gearing far higher than you'd expect in a vehicle of this size, the lusty little motor is spinning at just 2,000 revs when the car is travelling at 55mph, while a leisurely 3,000 revs takes the needle well beyond the 80mph mark. And even at that rate, easing off the power and adopting a trailing throttle produces amazing economy readings on the computer.
Yet again, this model highlights the benefit of a good power-to-weight ratio. Because the engine is so lightly stressed, the economy comes almost without trying.
Citroen provides the car with four seats, but rear occupants have to be tiny to fit in. Thankfully, that's not the case on the front row, where this clever little car provides ample room for 6ft 2in frames to travel in all-day comfort.
Appearances are deceptive, and the Citroen is a package that has capabilities far beyond the confines of the school run or short-haul commuting, even though ultra-low exhaust emission figures puts it in the AA road fund licence band and attracts an 18% BIK rating.
Regard it as a two-seater with handy load carrying potential via a split rear tailgate, and this car becomes a viable eco-model for long journeys. And parking it couldn't be easier when you get there.
Model: 1.4HDi LX
Engine (cc): 1,398
Max power (bhp/rpm): 70/4,000
Max torque (lb.ft/rpm): 111/1,750
Max speed (mph): 103
Fuel consumption (mpg): 68.9
Test average over 3,000 miles: 61.3mpg
Tank capacity (galls/ltrs): 9/4