Two-thirds of Americans collect reward miles and points for travel, but very few know how many points they have or how to use them. As a result, more than 25 percent of travelers are letting the miles expire.

This benefits the airlines, Brian Kelly, a world traveler and founder of ThePointsGuy.com told ABC's "Good Morning America."

"It's in the financial interest of the airline for you to let your miles expire," he said. "They make money when you don't maximize miles." The outstanding miles stand as a liability to the airlines.

"All those miles have to be accounted for," Kelly said. "That can affect their quarterly results."

A few airlines are addressing the frequent flyer issue.

Delta Airlines has changed it SkyMiles program so that when a person dies, their miles die with them, which was not previously the case. They're the first airline to have a policy like that. They also announced that this year they would start requiring a spending minimum in addition to the distance flown to earn miles, making it more difficult for travelers on a budget to even accumulate the miles in the first place.

Kelly, who makes use of his miles, flew first-class from Brazil for $2.50. However, he flies 150,000 miles a year.

Most travelers don't fly even close to that, and often don't acquire enough miles in a year to even earn a free flight. Those people are leaving "orphaned miles all over the place," Kell said.

You don't need to be a frequent flyer to earn miles, he said.

"If you're going to shop at Wal-Mart anyway, why not go through the airline portal to earn miles for your purchases?" he asks. "Travelers are sitting on hidden treasures.

"You need to treat your miles like money," he said. "Even if you only have 4,000 miles, use it to buy magazines, something."

Members of Delta's SkyMiles can go to skymilesshopping.com and earn a mile for every dollar they spend at Wal-Mart. Other lesser-known brands offer up to four miles for every dollar spent.

Kelly said it can be hard to keep track of miles and points and recommends travelers keep all their information in one place. He uses AwardWallet.com and TripIt. He recommends TripIt for a feature that sends you e-mail when miles are close to their expiration date.

Kelly feels that since travelers love to hate the airlines, the best revenge is to use their own programs against them.

"It takes a little time to figure out, but once they're all in one place, it doesn't have to be a full-time job," he said. "Having your head in the sand is exactly what they want."

That way, when you want your feet in the sand, you will have to pay more, and the airlines will make more.