BEND, Ore. (CNN/Money) - So many deals, so little time. No doubt that the Web is fertile ground for airfare bargain hunters. But now that there are more sites selling tickets than, frankly, we care to count, it's nearly impossible to know when you're actually getting the best fare available.

"Are you consistently going to get the best prices from any one Web site? No." said Edward Hasbrouck, author of "The Practical Nomad Guide to the Online Travel Marketplace." "It's important to try several sites with access to different types of airfares."

In fact, after exhaustive testing of the six largest integrated travel sites, Consumer Reports Travel Letter concluded that while Expedia, Travelocity and, to a lesser degree, Orbitz turned up the lowest "viable fares" (meaning flights that were close to the requested departure times and with few, and quick, connections), consumers still need to comparison shop.

Of course, there is some cost associated with finding the lowest fare and that cost comes in terms of your time. So, decide how committed you are to really finding the lowest fare then take it step-by-step, stopping when you think you've reached your limit.

Every search for low airfare should start at one of the travel supersites. Those are Expedia.com, Travelocity.com, and Orbitz.com. All of these sites give travelers access to vast databases of "published fares," coming directly from the airlines. These fares don't vary from one site to the next and are a pretty good indication of what tickets cost for a particular itinerary -- with two exceptions. Southwest Airlines does not sell tickets via any sites other than its own, and Jet Blue works only with Travelocity.

If you're looking for a specific itinerary or don't have a lot of time to track down tickets, you might simply search for the lowest fares on whichever of these sites you find easiest to use, book your flight, and call it a day.

If you're serious about finding the cheapest ticket, however, you'll want to explore all three of these sites. In addition to published fares, these online travel agencies are also privy to special fares they've each negotiated with the airlines. These specials are often only offered for a day or two. So whether you find the best price on Expedia, Travelocity or Orbitz depends on when you're shopping, where you're going, and when.

After trolling through all of these sites, you may find what you consider an exceptional fare. If that's good enough for you, stop here. If you're willing to invest a little more time to save more on your tickets, press on.

Once you use an online travel site to zero in on an airline with the best fare for a particular route, pay a visit to that airline's own site. In some cases, your effort will be rewarded with a slightly lower price or additional perks.

To reduce the volume of calls to their call centers and avoid paying commissions to the likes of Expedia or Travelocity, airlines use deals and freebies to entice passengers to buy tickets directly from their Web sites. According to Ed Passerella, editor of Smarter Living, these web-only extras can be anything from an additional 5 or 10 percent off the price, free or discounted companion tickets, bonus frequent flier miles or even free flights for booking online a few of times.

Because Southwest's fare information won't come up if you search one of the online travel agents, you might also want to make a point of checking its site, southwest.com. "A lot of times I find the discount airlines have the lowest fare, period," said Hasbrouck, noting that he's earned most of his recent frequent flier miles on ATA, another discount carrier.

Still not low enough? The final stop, if you want to go still further, should be at one of the sites offering so-called opaque fares. Hotwire.com and OneTravel.com, among others, allow you to search for the cheapest fare based on the dates you want to fly and the number of connections you're willing to make. Unlike Priceline.com -- where you name your price and the flight is automatically booked if a match is found -– these sites show you their best offer before you hand over your credit card information. Still, they don't reveal the name of the carrier or flight times until after you've committed to the ticket, and the tickets typically don't earn frequent flier miles or allow you to fly standby or upgrade.

"I would say that for flights within the U.S., if you really care about nothing other than price, 90 percent of the time the lowest price is going to be one of the opaque consolidated prices," said Hasbrouck.

Why does not knowing the name of the airline or the flight time before you buy save you money? It's not that the sites are putting you on no-name airlines, though they are probably putting you on flights with the least-desirable departure times. Rather, this is one way for airlines to separate the passengers who are willing to pay more from the passengers who are extremely price sensitive.

"The fact that you don't want to stay a Saturday night is a good indication that you're a business traveler, which is why flights without a Saturday night stay usually costs more," said Hasbrouck. "That you're willing to fly at any time with any airline is a pretty good indicator that you aren't willing to pay more for the ticket."

It's worth noting that both Travelocity and Expedia also offer opaque fares, but don't allow you to search for them exclusively. Instead, they sometimes show up after you've done a general search. Travelocity tags its opaque fares with a generic logo of an airplane rather than the airline's name or logo, and Expedia labels the fares "Expedia Bargain Fares."

If after searching the largest online travel sites, checking the airline's Web-only offerings and doing an opaque search, you're willing to go another step, you can always try naming your own price on Priceline.com. "For the ultimate price sensitive person if you've seen what prices are with Hotwire and other consolidators, you don't have anything to lose if you offer something below that," said Hasbrouck.

Nothing to lose except, of course, a little more time.