Which is more likely to save the planet, $75-a-barrel oil, or "green Dave" Cameron posing for pictures beside one of those cars which save petrol by running on electricity part of the time?
No prizes for the answer. The prospect of paying £1 a litre for petrol may well sell dual-fuel cars in serious numbers. But nobody is going to buy one motor rather than another because they have seen a snap of Mr Cameron leaning against the door.
There may not be much planet-saving in the decision, though.
Electricity used to charge dual-fuel batteries is generated by power stations that pump carbon dioxide into the atmosphere just like petrol (except the the nuclear ones, which churn out radioactive waste that nobody knows how to dump safely).
For planet-friendly motor-ing it is hard to beat a diesel because a gallon goes so much further. True, unless they are beautifully tuned, diesels throw out nasty particles that are said to give passers-by cancer - but without harming the planet.
The financial attraction of dual fuel is that two-thirds of the cost of petrol and diesel goes to Gordon Brown, while he gets only five per cent VAT on electricity. In time that could create a market for petrol/electric cars. Part of the motor industry is investing meaningful money in them, which it presumably hopes to recoup.
That is one welcome byproduct of pricey oil. It makes commercial sense of energysaving research - just as it gives oil companies an incentive to look for oil in places that used to be too expensive.
Or rather, energy-saving research and development should make commercial sense. For some reason, there is not a lot of it in Britain.
Last week the EEF, which knows what is going on in manufacturing, revealed that Britain spends only 0.02 per cent of its gross domestic product on energy R&D. That is one-tenth of what they spend on it in the US - where President Bush purports not to be bothered with such things. In the EU, only Portugal spends less proportion-ately than we do, according to the EEF.
Martin Temple, the EEF's director general, fears that Britain risks missing out on a chance to take a valuable technological lead.
He wants more generous tax credits for energy-saving Research and Development, along with better capital allowances for investment in e nergy efficiency and climate-friendly energy resources like "clean" coal.
There is logic in that - provided that the money is spent more sensibly than some other Government money. It would also do more for the Government's environmental credentials than Mr Cameron's photo-opportunities can ever do for the Conservatives.
One wonders, though, in this supposedly market-driven world why the investment isn't happening anyway. Do British boardrooms still doubt whether oil prices can stay for long at anything like their present prices?
Well, if this is a bubble, the only thing likely to burst it is a collapse of China's demand for oil - that is a collapse of American demand for Chinese goods, and much else besides. ..SUPL: