Besides reducing the weight and size of current automobiles, the other best solution to improving fuel efficiency is the diesel engine. While hardly the darling of the environmentalists since they still use pistons to squeeze fossilised dinosaur juice, the diesel has the greatest chance of getting drivers to significantly reduce their fuel consumption without compromise, if the engines are applied throughout our fleets, including in hybrids. That\'s doubly true with two recent developments, the first being the ongoing civilisation of the once-cranky diesel. Thanks to European manufacturers - stand up and take a bow BMW, Mercedes and Volkswagen - the turbodiesel, now fairly common in Teutonic offerings, is not just the equal of current petrol engines, but their superior. BMW\'s latest 335d, just to name one of many examples, has proven that oil burners can be both sporty and frugal. And, because they require no special transmissions, exotic-metal batteries or high-tension electrical cables, their initial price bump is less than hybrids. Even less so if the second development I alluded to bears fruit. Mazda, an unexpected source of diesel innovation, claims that diesel engines need be no more expensive to produce than conventional motors. Diesel engines have traditionally operated with fantastically high compression ratios compared with petrol engines. And while that has all manner of efficiency benefits, it means that their internal parts have traditionally had to be far more robust. Compare two equal displacement engines - Otto cycle and diesel - and the petrol engine appears almost delicate by comparison; parts are smaller and far less robust. All that costs money, much of the reason (along with the fact that many emanate from high-cost Germany) that diesels have commanded a price premium. But Mazda claims to have made an astounding breakthrough, saying it can make diesels run efficiently with similar compression ratios as petrol engines. That means diesels can use the same sized internal bits, be built on the same production line and cost roughly the same amount to manufacture. In other words, diesels could be offered on a widespread basis with little or no price bump, meaning that their miserly fuel consumption would provide an immediate payback. But the dieselification of our fleet need not be restricted to the conventional automobile. Hybrids, too, might be far more effective were their petrol engines replaced with diesels. Almost all of hybrid\'s fuel consumption advantage is gained in the urban cycle. On the motorway, their advantage is far less pronounced since they are essentially being motivated by the petrol engine alone. But motorway cruising is where the diesel\'s miserliness shines particularly bright. A Prius with a small turbodiesel instead of its current 1.8L petrol engine would surely get far better mileage. Plug-in hybrids would similarly benefit. Even the Chevrolet Volt\'s performance would be greatly improved as its one weakness - besides price - is its fuel economy once its lithium ion batteries run out of electrons and its on-board Ecotec engine takes over the generating duties. Diesels have long offered an answer to our desire to reduce fuel consumption. They do so with few compromises and, if recent developments filter through the industry at large, with very little price penalty and with immediate cost savings. And, in the end, whether environmentalists want to embrace diesel technology or not, for many consumers nowadays, reducing fuel consumption is all about saving money, not the environment.