Opponents call them unsafe gas guzzlers that are bad for the environment — but that hasn't stopped Americans from eagerly snapping up more and more SUVs each year.

In fact, sport utility vehicles (search) have increased in popularity, with sales up almost 7 percent in 2002 and up 42 percent over the past five years, according to industry figures.

So what's behind the boom?

"The reason people buy sport utility vehicles is because Americans like big cars," said Aaron Robinson, technical editor for Car and Driver magazine. "They equate value with size. And a lot of people feel safer in them."

There's also a certain lifestyle associated with the SUV that Americans find attractive, according to Robinson.

"There's a definite image associated with sport utilities that turns people on — the youthful, I-can-go-anywhere-and-do-anything image," he said.

Revenue figures show that sport utility vehicle sales have spiked significantly in the last decade-and-a-half. In 1988, only 960,852 SUVs were sold in the U.S., accounting for 6.3 percent of all sales of light vehicles, according to The World Almanac. In 2001, the numbers had jumped to 3,787,250 SUVs sold — 22 percent of all light vehicles.

The bevy of campaigns about SUVs polluting the air and being likely to roll over in accidents doesn't seem to have had an impact on what Americans are driving.

"You can tell people 'til you're blue in the face," Robinson said. "I think by and large, consumers just aren't swayed by the safety and environmental arguments against sport utility vehicles."

SUVs are more likely to have rollover accidents than cars. According to the National Highway Traffic Safety Administration (search) (NHTSA), 61 percent of all SUV fatalities in 2002 involved rollovers, a 14 percent increase over the previous year.

But SUV owners and their passengers are actually statistically safer in accidents than the drivers and passengers of smaller cars — a major reason SUV drivers give for buying the vehicles.

For every person killed in an SUV involved in a side-impact crash with a car, 22.1 people are killed in a car, according to the NHTSA. For every person killed in an SUV in a head-on collision with a car, 4.5 people are killed in a car.

Those same statistics have fueled the safety argument of the anti-SUV movement.

Opposition groups like Earth on Empty (search) continue to campaign against the vehicles on the grounds that they jeopardize other drivers' safety, guzzle gas, spew unhealthy fumes and clog traffic because of their size.

"They epitomize America's disregard for energy conservation," said organization founder John Tagiuri. "They're polluting your air, threatening your life and affecting foreign policy. They're encroaching on other people's freedom."

One of the more recent SUV crazes and controversies has been over the Hummer — a massive General Motors (GM) vehicle modeled after the military Humvee (search), which became famous during the Gulf War.

But behemoth trucks are already becoming passé. Robinson predicted new, smaller varieties of sport utility vehicles will gain ground and drive the sector's growth in the future.

"You're going to see more variations of the SUV — crossover vehicles that are half car, half truck; light SUVs and so on," he said. "The image of a giant, hulking SUV is to a certain extent becoming outdated. More and more people are buying smaller sport utility vehicles."

Auto giants like Ford Motor Co. (F) are banking on the crossover SUV as the next big thing.

"There's a continued growth potential, especially for crossover vehicles that offer a combination of features," said Jon Harmon, public affairs manager of Ford Division.

Ford makes an array of sport utility vehicles, including the Explorer, the Escape, the Expedition and the Excursion. On the way next year is another model called the Freestyle, according to Harmon.

"The SUVs offer customers what they're looking for in terms of being versatile and able to haul around a lot of people and gear," he said. "They offer customers the ability to go anywhere without leaving anything behind."

Earth on Empty's Tagiuri is dismayed by the SUV boom, and said it's largely thanks to all the advertising dollars the automotive industry has put towards marketing sport utilities.

"They have spent more on advertising than (has been spent) on any of the top 10 products put together," he said. "They have got a cash cow here and they're going to milk it."