By Samantha Bomkamp, AP Transportation Writer

NEW YORK (AP) — Fly to the Bahamas today for $10. Take a trip to Los Angeles tomorrow for $20. While airfares generally are higher these days, last-minute sales that ask you to fly at a moment's notice are popping up everywhere.

Why do airlines launch a sale that asks people to travel the next day or fly on off-days like a Monday or Tuesday? The biggest reason boils down to simple supply and demand: More people are flying, so the airlines don't need to launch big sales on more popular days. That's especially true with the summer travel season approaching.

But there's more to it. Here's a look at why the airlines offer last-minute sales and how best to take advantage.

First waves of last minute

Last-minute fare sales are here to stay, at least for summer, according to Rick Seaney or Here's why: Facebook and Twitter.

These "fly on a moment's notice" sales are geared toward the instant communication of social media sites, which are rapidly overshadowing e-mail as an alert system.

JetBlue, which has one of the biggest footprints on social media sites among U.S. airlines, announced a sale last Monday for travel on Tuesday and Wednesday.

This type of sale is only going to grow in popularity, Seaney predicts.

Last-minute sales aren't generally ideal for travelers, though, because they force you to make your mind up fast and often travel at off-peak times. But the alternative — a longer sale where the airline may sell out too early — isn't great for travelers, either.

Eight to 10 months ago, last-minute sales were a rarity. Before that, airlines took weeks to review marketing and advertising plans prior to launching a sale. It's a much more organic process now that airlines have realized the potential free marketing social media provides.

United, for example, launched a contest on Twitter this week that required its followers to "retweet" sweepstakes rules to be entered into a ticket giveaway. (Translation for the social media novice: tell all your friends, and we'll let you play.)

Homework counts

What do more last-minute deals and fewer sales overall mean for travelers? More homework.

If you don't know the average price of a trip to Grandma's, you probably won't get the best deal. And if you're not flexible, you'll likely pay a lot more than you did to take the same trip a year ago.

Overall, ticket prices are about average with fares before the recession. Still, some consumers may have sticker shock because they grew accustomed to cheap tickets and extended fare sales when travel demand was sluggish.

Sales in general are becoming more scarce. For example, discount carrier Southwest hasn't had an across-the-board fare sale since November of last year, Seaney said. At the height of the recession, it had nearly one sale per week.

The bottom line

It's going to take longer to spot deals this summer. And fares will likely be higher this fall, too, so you'll have to know how and when to find bargains.

The keys: Start looking at prices online three months before you want to travel. That's when airlines start to manage their seats. More than three months out, airlines haven't figured out which tickets are selling and which aren't, so they generally won't cut fares. Within that three month timeframe, waiting too long might put you out of the running for the cheapest seats.

That doesn't mean you should buy right at the three month mark, but starting to research at that point will give you a good idea of what the ticket will cost you. That way, if a last-minute sale pops up for the destination you're looking for, you can jump on it.

Seaney says consumers should be prepared for sales that last no more than 5 or 10 days during the summer months.

And remember the cardinal rules of fare shopping: The best time to shop is Monday or Tuesday, not on the weekends. Wednesdays, generally, are the cheapest days to fly.

Copyright 2010 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

—For the best rates on loans, bank accounts and credit cards, enter your ZIP code at