As the number of hybrid cars continues expanding, comparing them becomes evermore daunting. Trying to make sense of all the numbers can be akin to sifting through the tiny print in an insurance policy.

To simplify the task, we've selected several key cost and efficiency categories to use in making preliminary comparisons if you're shopping hybrid cars.

We have included only full-hybrid, or HEV, passenger cars -- those that can use their electric motors for propulsion -- currently in dealer showrooms. Mild hybrids, such as the Chevy Malibu Hybrid, are excluded because their batteries are used primarily to operate the electrical systems when the gas engine is automatically shut down at a red light. Plug-in hybrids, or PHEVs, such as the Chevy Volt, are not yet on the market.

Hybrid technology is expensive, so what's considered entry-level-priced hybrids, such as the Honda Insight LX, start at about $21,000.

However, the cost of owning and driving a hybrid car encompasses far more than just the manufacturer's suggested retail price or even the actual purchase price. We've made our cost comparison on total cost and cost-per-mile over a five-year ownership period -- all assuming the car is driven 15,000 miles per year.

Reducing pollutants is another key reason for considering a hybrid. There are two types of pollutants found in vehicle exhaust: those that contribute to smog and greenhouse gases that trap heat in the atmosphere. Because most hybrid cars put out less than 3 pounds of smog-producing pollutants per year, we are including only greenhouse-gas emissions in this comparison.

As a starting reference point, consider that the four-cylinder gasoline-powered Toyota Camry expels 5.68 tons of greenhouse gases each year, while the Lamborghini Gallardo Coupe spits 9.22 tons into the air.