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Regular readers of this column know I love frequent-flier miles, and I'm always on the hunt for ways to get more.

That's because frequent-flier miles turn into nearly free airline tickets that make my family vacations affordable.

Miles also can be used to pay for hotel stays, rental cars, and a variety of other things, including magazine subscriptions.

Miles are a form of currency, and airlines use them as incentives for credit card offers, to promote miles-for-dining programs and to encourage people to do their online shopping on airline-affiliated websites.

But does it ever make sense to buy miles outright, or pay to transfer miles, as airlines encourage people to do?

I was pondering that question last week, shortly after returning from a ski trip to Denver that was made possible with mileage award tickets.

I found that US Airways and Delta Air Lines are now promoting temporary incentives for buying or transferring miles, and having depleted my accounts, I thought I'd check that out.

Buying miles involves paying the airlines to add miles to your account or someone else's, while transferring miles involves paying the airline to move existing miles from one account to another.

I think the mileage-transfer deals could be appealing in some circumstances.

For example, let's say John and Mary want to fly somewhere together, and are looking for ways to reduce the cost. They each have Delta or US Airways frequent flier accounts with 10,000 miles each, but they need 25,000 miles for one award ticket.

Both airlines are currently offering mileage transfer promotions that reduce the usual cost of sharing miles. The usual rate is $10 per 1,000 miles, plus a $30 fee, plus 7.5 percent tax, which works out to $140 to transfer 10,000 miles.

Here are the deals:

Delta: Through June 30, get a 50 percent bonus on mile transfers. It would still cost $140 to transfer 10,000 miles, but the recipient would get 15,000 miles. That means John and Mary could turn their two accounts with 10,000 miles into one account with 25,000 miles.

US Airways: Through May 14, get a 75 percent bonus on one mileage transfer. John and Mary would only need to transfer 9,000 miles in order to get 15,750, and the cost would be reduced to $129. (Miles must be transferred in 1,000-mile increments).

Is it worth spending the money to transfer miles? That depends on the out-of-pocket cost of the plane ticket you would use the miles to acquire.

Mileage transfers could also be useful in a situation where a person, maybe an elderly relative, no longer wants to travel by air but still has airline mileage accounts. They might transfer miles so that a relative or friend could come for a visit.

What about buying miles?

My curiosity was piqued when US Airways pitched a 50 percent off sale on mileage purchases for people who have one of the airline's credit cards.

US Airways normally sells frequent flier miles for $27.50 per 1,000 miles. Delta charges $28, and in both cases there's also a 7.5 percent federal tax.

I can't think of a situation where it would make sense to buy miles at that price.

You'd be looking at about $750 for 25,000 miles, and those miles could only be used for hard-to-find minimum mileage award tickets.

You could probably buy the plane ticket for half the cost of buying the miles.

Most of the buy-miles deals are meant for people who are a few thousand miles short of what they need for a free ticket. But at those prices, I wouldn't buy even a few thousand.

But what about promotions such as US Airways' 50 percent off sale?

In that offer, if you have a US Airways credit card, you can buy miles at half-price through May 14, and with some of those credit cards, you already get a 5,000-mile discount on the miles needed for a ticket.

So, you would need a minimum of 20,000 miles for an award ticket, and you could buy that many miles at the discounted rate for $296, including tax. Now that's more like it.

At $14.78 per 1,000 miles, including tax, I would consider buying miles if I had an immediate use for them that would work out cheaper than buying a ticket directly.

Reach David Slade at 937-5552. For more money-saving tips, go to postandcourier.com/personal_finance.