US Airways is offering a 100% bonus on purchased or gifted miles through July 31.

Leave it to US Airways’ marketing genuises to say that a mileage purchase promo that runs from June 1 through July 31 is “for one month only” — but the bonus indeed runs two months.

The maximum bonus is 50,000 miles for buying 50,000 miles, and 100,000 miles gets you business class fro the US to Europe (90,000 gets you business class from the US to North Asia including Hong Kong).

This year US Airways raised the price of miles from 2.5 cents apiece to 2.75 cents apiece, and also the mileage cost of several awards. So we’ve gone from $1000 in purchased miles for business class to Europe to $1400 for the same. Still, with the ability to redeem Star Alliance awards on so many Lufthansa routes so easily it’s still a good deal for many — especially because US Airways permits you to put an award on hold for 3 days without the miles in your account, and then you go about purchasing the miles.

One caveat, back in November and December the offer required that an account be open for a week before being able to earn the bonus. I don’t see that requirement in the terms and conditions of this offer. But if it were me until I had verified this I would make sure my US Airways Dividend Miles account was open for 8 days before purchasing miles — even if the terms and conditions don’t say it, and presumably you’d be able to successfully argue for the miles — there’s some chance that the previous programming for the offer remains in place.

Note further that this offer is stackable with the 25% bonus on purchased miles for US Airways elite members.

In April and May US Airways was offering double miles on transfers. Indeed, as Flyertalk’s ArizonaGuy observes, US Airways has offered a 100% bonus on purchases, transfers, or both in 9 of the past 12 months. They’re monetizing these miles, scooping in cash, and the fact that they continue to offer these bonuses suggests that it’s successful.