Strange how things go sometimes. Not long ago we were bemoaning the fact that there were not enough gas refuelling stations around the country where we could fill up our LPG-powered cars.
Now we've got more than 1,000 sites across the UK, but the number of LPG offerings from manufacturers seems to be falling.
I noticed this when I came to do some number crunching for this road test. Surely, I thought, there must be a competitor for Volvo's LPG-powered S80 executive saloon. Well, there isn't, because Vauxhall has discontinued production of the DualFuel Omega range.
As no other manufacturer in this sector offers LPG, I have taken the unusual step of comparing three cars from the same manufacturer in this test.
Firstly, we have the Bi-Fuel S80 which has a liquefied petroleum gas tank as well as the regular petrol tank.
This model is based on the second car in our test, the S80 2.4 S petrol model in 140bhp guise.
To complete the line-up is the diesel-engined S80 2.4 S fitted with Volvo's excellent D5 engine. So rather than discovering which LPG-powered car is the most cost-efficient for your fleet, instead we're going to discover which type of fuel is the most cost-effective for your fleet instead.
In terms of front-end price, the LPG model is the most expensive, adding more than £2,000 to the price of the 2.4 petrol model in S spec. The diesel also has a price premium, although it costs £500 less than the LPG car.
But front-end price competitiveness is nothing without a healthy residual value prediction to back it up.
The experts at CAP Monitor appear to echo the trade's wariness of LPG-powered cars, predicting the Bi-Fuel will retain just 30% of its cost new after the typical three-year/ 60,000-mile fleet benchmark.
By comparison, the petrol model is predicted to retain 34% over the same period, while the D5 reflects diesel's current popularity with the highest residual value prediction of 37%.
This helps the D5 record the second lowest depreciation cost of our trio of 21.94 pence per mile, compared with LPG's 25.12 and petrol's 21.18. All three are roughly similar on servicing, maintenance and repair costs (ranging from 2.79ppm to 2.95ppm) but the biggest difference comes with fuel costs, the real crux of this road test.
Leading the way is the Bi-Fuel, which costs 7.91ppm. While it may only record 25.2mpg on the combined cycle, LPG's cheap price (roughly 38pence per litre) more than makes up for its poor economy performance.
However, the D5 diesel is not far behind, costing 8.36ppm thanks to a combined economy figure of 43.5mpg. In this company the standard 140bhp petrol-engined model is outclassed, recording 31.7mpg on the combined cycle for a fuel cost figure of 12.04ppm.
All three are also pretty close in terms of monthly rental charges, with HSBC quoting £445 for the D5, £477 for the Bi-Fuel and £424 for the petrol.
For VED rates, the diesel costs £130, the Bi-Fuel £150 and the petrol £155. So far, things are going in favour of the diesel, but surely the Bi-Fuel will even things up by being more attractive to drivers through reduced benefit-in-kind tax?
Well, almost. LPG cars get a 1% discount on the sliding scale of petrol cars, meaning the S80 Bi-Fuel falls into the 18% banding for 2002/03, compared with 24% for the petrol model and 19% for the diesel.
DESPITE all the potential for confusion over discounts on VED and benefit-in-kind tax and the cheaper fuel, the Bi-Fuel S80 loses out to its more conventional diesel stablemate.
The S80 D5 stacks up from a running cost point of view, has the lowest levels of carbon dioxide emissions, the best fuel economy and the highest residual value predictions of this group.
Volvo should be applauded for making the Bi-Fuel option available, but it should really only be considered by fleets which are keen to make a strong environmental message.
Behind the wheel
'NO noticeable loss of performance when running on gas', trumpets Volvo's promotional blurb for the Bi-Fuel S80.
And this is true - you can't tell whether you are running on petrol or LPG. But that doesn't make up for the fact that the 2.4-litre engine's 140bhp power output is not up to the job of hauling this big and heavy car about.
Our test model was mated to an automatic gearbox which did its best to blunt any performance the engine could offer, making jerky downshifts to get any forward momentum.
The opposite is true for the diesel-engined D5 model, which has so much torque on offer that performance is quite lazy in comparison. We at Fleet News are very familiar with the D5 engine, having run one in an S60 for a long term test. Not only does it provide effortless cruising potential, but we are regularly recording a combined mpg figure of about 42mpg.
That is impressive for a car with more than 160bhp and such long-legged cruising ability.
The standard petrol model feels much the same as the Bi-Fuel model - underpowered for its size. The S80 has never really been a big hit in the executive ranks, but while it may not have the prestige German badge, it is a solidly built car with bags of space for all passengers and a comfortable ride.
Sitting in the driver's seat, the S80 is pure Volvo which means a large, plastic centre console which is angled slightly into the driver. This houses the stereo and climate controls, as well as various assorted buttons.
IF Volvo offered the Bi-Fuel option with the 170bhp petrol engine things might be different here. As things stand, the D5 diesel not only wins the fleet case (left) but it also wins the driving section too.
You simply can't argue with what is one of the best diesel engines on the market, offering 163bhp, plenty of performance and competitive running costs.