(MONEY Magazine) – LAST CHRISTMAS, MY FRIEND SUZANNE in New Orleans sent a gift package to me in New York City by priority mail. The U.S. Postal Service advertises the two-year-old priority mail program as a "two-day service to most domestic des- tinations," comparable to United Parcel Service's 2nd Day Air and FedEx's two-business-day service. All in all, priority mail seems like a bargain. Though it costs about three times more than regular first-class mail for items that weigh four ounces or less, the charges are about half the cost of UPS or FedEx. Only problem was, in my case, Suzanne's package didn't arrive in two days--or in 100 days, for that matter. Worse, when we tried to locate it, postal workers told us there was no way to trace priority mail. All we could do was file a claim and hope that it turns up. It hasn't.

Was my wayward gift a fluke in an otherwise reliable service? To find out, I and four MONEY correspondents in Chicago, Houston, Iowa City and Los Angeles mailed a total of 72 four-ounce envelopes to one another over a two-week period in February. We sent 32 of them by priority mail (cost: $3 each) and 40 by first-class mail ($1.01 each). All five cities supposedly get two-day priority service.

None of these envelopes disappeared. Still, priority mail came off looking like a waste of money. Of the 32 "priority" envelopes, only half arrived within the promised two days. Six took fully five days to arrive. On average, it took three days for each priority envelope to show up--practically indistinguishable from the 3.4 days it took our average first-class envelope. The distance the package had to cover bore no relation to whether it arrived on time or not.

"We make every effort to deliver priority mail within two days, but two-day delivery is not guaranteed," says U.S. Postal Service spokesman Frank Brennan. "We are at the mercy of the commercial airplanes that carry the mail." In fairness, severe snowstorms during the first week of our test undoubtedly played a role in the delays. However, there were just as many late priority envelopes during the second, more clement week.

Our conclusion: If you're not in a rush, stick with first-class mail. If your missive absolutely must get there fast, pay one of the commercial overnight services to deliver for you.

--Elif Sinanoglu