We see and hear about them everywhere. From newspapers to the internet to the blogosphere, hybrid cars are everywhere. From the recent 2010 Paris Motor Show, where it seemed as if almost every mainstream automaker had one on display, it's more clear than ever that automakers the world over are now investing serious time and money into hybrid development. Within the past decade, the number of hybrid cars on the road has risen steadily.

According to estimates by the Department of Transportation, about 1.5 million hybrids were sold in the US between January 2004 and December 2009. With such marketing and PR pushes like the Paris Motor Show, it's inevitable that number will climb even higher. While it is certainly true that hybrids get better fuel economy than their purely gasoline-powered counterparts, in comparison tests with diesel-powered cars, however, the results are less clear. Diesel can give fuel economy numbers which are, at the very least, competitive with hybrid numbers.

They can achieve this without the use of environmentally questionable nickel metal hydride batteries as well, and this raises some questions. Diesel-powered cars (trucks aren't in this debate) don't sell in anywhere near the same numbers as hybrids do in the US, and most people who buy hybrids never even consider a diesel. The recently launched myvolt.com hinted at what might be the real reason behind the relative popularity of hybrids. The site is for Volt owners and includes a feature which allows them to post their mileage reports on Facebook or Twitter.

Going green seems to be the new conspicuous consumption and saving the environment only matters if people can see you doing it. The fashionable hybrid badges that are slapped all over the Prius are absent on the Jetta TDI and sales figures reflect the TDI's hipness deficit, despite its high mpg numbers. Diesel lacks the excitement that the newness of hybrid technology can offer, to say nothing of the stigma which diesel still has to shake off in the US. They don't come with the cool driver information displays from the Prius.

As such, the extent to which you're saving the planet is less obvious. We would never suggest that hybrids aren't good for the environment, but perception is a powerful force in the marketplace, and it means everything to those who worry about what their purchases say about them. Cameron Diaz's famous (and somewhat dubious) 52 mpg in the city claim did more for Prius sales than any EPA mileage report ever could. Let us be clear: we're not denying the positive impact hybrids have on the environment.

In fact, we're thrilled to see more car buyers making the change over to them because they care about the effects of global warming due to high emissions and ever growing oil costs. Just remember that diesel offers an alternative to the alternative of hybrids. Stay tuned next week as we tackle the even trickier subject of electric cars.