If you don’t mind flying blind, purchasing your travel needs from an “opaque” Web site could save you a bundle.

Unlike “transparent” travel sites such as Expedia.com and Orbitz.com – which identify the service providers with whom you’re dealing – opaque sites Hotwire.com and Priceline.com won’t tell you the company you’re doing business with until you enter your credit- or debit-card number. By then, what you see is what you got: Everything is final, with no refunds or exchanges.

Hotwire and Priceline act like the clearance racks of the travel industry: They get the flights, rooms and cars that the airlines, hotels and car-rental agencies are trying to unload quickly. Markdowns can top 40 percent or more.

We recently tried both sites to see which turned up the best deals. We also compared them with Expedia, Orbitz and Travelocity.com, another transparent site. First, we identified five itineraries for which we wanted to rent cars. We then went to Hotwire.com for rates on a car in five different cities on five different dates. We took the prices at Hotwire and chopped 25 percent off to start bidding on identical itineraries at Priceline.com. In four out of five tries, our successful bids required modifying our requests, which added 10 to 20 minutes to our shopping time. (You can’t rebid for the same itinerary within seven days, so we chose to upgrade or downgrade vehicle types from, say, economy to compact, instead of changing dates or locations.)

For all five queries, Priceline offered the lowest rate. Hotwire was usually the runner-up, although in two cases Orbitz matched Priceline’s bargain rate. (In both those instances, Priceline offered a car from Hertz, while Orbitz vendors were second-tier operators.) We also threw Priceline’s recently launched transparent site into the mix. It failed to find lower prices than Expedia, Orbitz, or Travelocity.

These results mirror a 2003 study of opaque travel sites by Consumer Reports WebWatch, a grant-funded project of Consumers Union, nonprofit publisher of Consumer Reports magazine. In that study, Priceline.com led seven travel sites – including Hotwire.com – by providing the lowest rate on airfare, hotels, and car rentals 47 percent of the time. Some savings totaled hundreds of dollars.

Here are some suggestions to help you maximize your savings on opaque sites:

¢ Get the inside scoop. Find shopping and bidding tips from other travelers by visiting sites such as BetterBidding (www.betterbidding.com).

¢ Shop the big sites. Before you head to the opaque sites, get a handle on market rates at Expedia, Orbitz, and Travelocity, as well as at sites run by airlines, hotels, and car-rental companies. Make sure that you nail down total prices, including taxes, surcharges, and booking fees.

¢ Don’t lowball. If you do, you’ll add steps to the booking process at Priceline.com. Of course, you don’t want to overbid, either. A good opening bid? Up to 80 percent of Hotwire.com’s rate.

¢ Charge it. If you use Visa or MasterCard, you won’t pay for services you don’t get. (If, for example, a hurricane destroys your hotel.)

¢ Keep your receipt or confirmation. You’ll need it for proof of purchase just in case the Web sites and the travel suppliers mix up your itinerary.

Although opaque sites can cut your costs, they’re not the best choice for every trip, especially if you have your heart set on a specific hotel or if you must follow a set schedule, since times and even dates could fluctuate. If you’re flexible but uncomfortable with not knowing where you’ll end up staying or which airline you’ll be flying, visit the “partners” sections on Hotwire and Priceline to get a list of their airlines, hotels, and rental-car agencies. Most are big brand names.