Thinking about buying a hybrid? How about a diesel or maybe just a subcompact? How do all these options compare in terms of purchase price, fuel economy, greenhouse gases and air pollution?

Hybrids have become synonymous with fuel economy and environmental activism - they sip gas and make a statement, all at once. Europe has invested heavily in clean diesel technology with awesome gains in average fuel economy; with California diesel fuel now up to European standards, some of these clean diesels will be on sale in the state in 2008. Then there's the subcompact - small & economic, it's a bare-bones car and a staple of miserly commuters.

We decided to do a side-by-side comparison of some of the most efficient new and used cars from each category (with a Suburban included for reference), to determine which approach is best for saving you money and sparing the environment. The analysis looks at three criteria: purchase price, fuel economy (which is directly related to CO2 emissions) and emission ratings. Below is the list of cars, ordered by fuel economy; scroll below the table for the assumptions made in compiling this list.

CA Emission Standard: this standard describes the amount of smog-forming pollutants such as Reactive Organic Gases (ROG) and Oxides of Nitrogen (NOx) produced by the vehicle; it does not take into account greenhouse gases. The highest (cleanest) standard is ZEV, followed by PZEV and AT-PZEV, SULEV, ULEV and LEV.

Using the purchase price and economy values in the above table, we plotted the total operating cost (excluding maintenance) for each of the cars over the course of 200,000 miles. This way, a car which has higher up-front (purchase) costs but eventually becomes a better buy by saving you money on fuel in clearly visible.

Looking at the results, it's clear that given the current fuel prices ($3.50, Dec 2008), hybrids do not offer cost savings over a cheap economy vehicle. Hybrids come with a large price premium, sometimes costing up to twice that of a small new car. That premium is not easy to justify: unless you plan on putting between 200,000 and 500,000 miles on the car (or gas prices radically increase), the purchase price premium will not be offset by the increased economy. You'd have to drive the Civic Hybrid, for example, a whopping 200,000 miles before it begins saving money over the 28mpg Ford Focus. Ironically, the two winners of the above comparison (the Honda Insight and the Geo Metro) have been discontinued by their manufacturers!

During this analysis another topic came up: what about the urgency of global warming and the need to do everything possible to burn less fuel (i.e. drive to most efficient car possible)? Good point, we thought, and one that seems to favor the hybrids, regardless of their cost premiums. The answer to this dillemma is simple and comes in the form of carbon offsets: hybrids are a way to mitigate global warming, but a very expensive one - the price premium spent to purchase a hybrid would be much more effectively spent by a (trusted) GHG offset fund to, for example, retrofit an old power plant.

That said, purchasing hybrids helps fund the technology, allowing it to mature and, presumably, become more affordable. Without a public interest in hybrid cars, we probably would not have hybrid buses!

For basic economy and emissions information, visit the EERE Fuel Economy page. To run a side-by-side comparison of any two vehicles, visit the DOE Hybrid Vehicle Cost Calculator. This is a great tool which takes into account vehicle relsale values and variable maintenance costs - it is highly recommended for making purchasing decisions! The EPA Green Vehicle Guide is usefuel for side-by-side comparison of several vehicles and has a combined GHG/pollution ranking system (SmartWay).

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