''Opaque'' sites are ones where you don't see the name of the supplying hotel or airline until after you've booked. At least, that's what they used to be. Today, the two sites offering ''opaque'' booking -- Hotwire and Priceline -- also offer choices where you can see the supplier up front. Bookings are nonrefundable, though some can be changed for a fee.
One tip: Experts say that both sites offer great deals on rental cars -- one travel commodity where one major supplier is much like the next.
Note that deals booked through these sites usually don't allow you to earn frequent flier miles or rewards points.
Here's the latest on each:
Now owned by Expedia, Hotwire offers ''opaque'' purchase options on flights, hotels and car rentals -- though prices are disclosed before you book, with no bidding. When it comes to cruises and vacation packages, you see all details up front. In some cases, ''retail'' options -- where you see the name of the bidder before you book -- are also shown for flights and car rentals, but it depends on the specific search.
Cool tools: When you book a flight, a new tool allows you to stick with the original flight plan or see how much you would save by changing to a nearby airport or alternative dates. TripStarter (reached from the home page), allows you see a graph of prices throughout the year on trips to specified destinations. The Local Trips feature on the home page helps you find hotels within a specified distance from your zip code.
E-mail newsletter: Yes, by subscription. Deals on ''travel ticker'' are paid placement but should match certain objective savings standards to be included.
Phone support: 24/7 -- though you may have trouble finding the phone number on the web site. (866-HOTWIRE). During U.S. business hours you get U.S.-based agents; agents are off-shore during other times
The best deals still come from ''name your own price'' specials, says Brett Keller, chief marketing officer -- up to 50 percent off regular rates. (And yes, they all come from major suppliers -- including American Airlines -- and major hotel chains, though not Ritz-Carlton or Four Seasons. Air rules mean you have a maximum of one connection and a layover no longer than three hours.)
Bidding rules mean that if your bid has been turned down, you can bid again only by changing one of your parameters -- star-level, neighborhood or date -- or you must wait another 24 hours.
And there's help: The independent website, www.biddingfortravel.com, posts the amount of recent winning bids, so you're not completely in the dark.
Group hotel bookings are also offered.
Disclosed prices: If you don't like guessing games, Priceline now offers options where you can see the price and often, the supplier as well.
Hotel searches deliver two types of results: those with price and neighborhood but no name, and those with the hotel name and address. Zagat hotel reviews are integrated throughout the site, so they're easy to check as you're surfing.
Flight searches show the airline and all flight details.
Car searches show prices and brand. This is one area where you may be better off with the ''name your own price'' option -- because all cars are offered at the airport and come from one of five major brands. (Bid about 30 percent less than the disclosed price.)
On vacation packages, tours and cruises, all details are shown in advance of booking.
Rewards program: The more you book, the more you receive -- but there's no set dollar for dollar or point for dollar system.
E-mail deals: Yes, by subscription. A mix of deals chosen by staff and those purchased by advertisers.
Phone support: Yes, 24/7, for confirmed bookings (800-774-2354) -- though you're supposed to e-mail them first. Agents are U.S.-based.
Mobile-enabled functions: Yes