NEW YORK » For travelers who aren’t tapped out from the holidays, it’s a great time to fly.

January and February are the slowest travel months of the year. Planes that were packed during the holiday travel season could be just half to two-thirds full.

To fill their empty seats, airlines are offering abundant fare sales and ticket prices lower than those in recent months. AirTran and Southwest, among others, have launched widespread sales. Other airlines are running more low-key offers.

Fares for flights through mid-February can be as much as 50 percent lower than summer ticket prices. But they’re higher than this time a year ago, and likely to rise again soon as airlines cover higher fuel costs. So, would-be fliers will still have to do some homework.

Many winter sales are unadvertised. George Hobica of travel website airfarewatchdog.com says these so-called retaliatory fares are common in slower travel periods as airlines fighting over a limited number of customers try to undercut one another.

Hobica says travelers need to set up fare alerts and carefully research prices to ensure they catch these stealth sales.

You can set alerts on airline websites, online booking sites Orbitz and Expedia or other travel sites like Travelzoo or TripAdvisor. It’s best to use more than one.

The routes with the most airline competition are where travelers will find the best deals. Currently, that includes flights between Denver and the East Coast and between Los Angeles and Las Vegas. Flights between L.A. and Vegas are as low as $38 one way, Hobica said. That’s less than an average tank of gas. Or the cost of checking two bags.

In general, any flights to warm-weather destinations are your best bets for winter deals, he said, including California and some parts of the Caribbean.

But buyers beware: A sale fare might seem flashy, but sometimes another airline’s regular fare will be cheaper. The key is to monitor the cheapest prices to your favorite destinations. When a deal pops up, you’ll know whether it’s a good one.

This will also keep your expectations realistic. Fares on nearly all domestic routes are higher than they were last January.

"We get these e-mails saying, ‘Sale, sale sale!’ but (the advertised fare) used to be the actual prices," Hobica said. "I think people have to rethink what a low price is."

A flight between New York and Los Angeles a year ago, for example, would have been as low as $198. That trip cost upward of $500 over the holidays, and fares for March travel and beyond are similar. The cheapest price for that flight in February is just over $300.

Fewer travelers means less crowded planes. So, assuming good weather, your flight is more likely to be on time because it’s quicker to board a plane that isn’t full. Overbooking is also less likely, so gate agents don’t have to spend time looking for volunteers to take a voucher for another flight.

And the deals don’t just stop with low ticket prices. You’ll also see less expensive hotel rooms and rental cars. Book your flight, hotel and car (if you’ll need one) together to save the most money. Online booking sites often secure deals that aren’t available to travelers purchasing parts of their trip individually.

And act fast: Airfares and other travel costs start to climb around Feb. 15, synched up with many school vacations. They bump up again at the end of March, as the spring travel season begins.