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Car insurance companies are aggressive in boasting about their discounted rates, but which ones offer the most?

Bankrate.com put together a list of 17 discounts that car companies offer, such as a discount for having an anti-theft device for your car or being a member of the U.S. military. Of the 10 companies studied, Farmers offered the highest number of discounts at 16.

"The cost of car ownership isn't getting any cheaper these days, and gas prices are stuck above $3 a gallon," said Bankrate's insurance analyst Doug Whiteman. " It's important to get whatever discount you can."

Bankrate found that 10 major car insurance carriers provided a discount for having multiple policies with that carrier. Eight of the 10 major insurers charge less for paperless billing.

Not all the discounts are clearly advertised, some of which can be found in question-and-answer sections or blog posts, said Whiteman. Some discounts are particular to certain states or by location. For example, some carriers offer discounts to young drivers attending school at least 100 miles from home, which is known as a distant student discount.

"The idea is if your kid is away from school, he or she is much less likely to be driving the family car, so you can get a break on your insurance," Whiteman said.

And there are even more discounts that Bankrate did not track, Whiteman said. Some carriers might have discounts for new parents, or those who own a home.

"It's a really good idea on a regular basis to review your car insurance policy, maybe at renewal time," Whiteman said. "Some companies better at advertising discounts than others. In some case you have to talk to someone on the phone."

Here's Bankrate.com's cheat sheet for car insurance discounts you may be missing:

(Image credit: Bankrate)