There are two promotions going on currently which can help you earn United Miles at ~1.8 cpm (cent per mile). Although this might not be a cool way to earn united miles, but if you are short of miles for you next award and want to get there quickly this could be for you rather than buying it directly from united at a cost of ~3.5 cpm.
There are currently two promotions going on which both co-incidentally run till November 30th, 2013.
Wyndham points can be purchase in the blocks of 1000 points with each 1000 points costing $11. So let's say you purchased 20,000 Wyndham points you would essentially pay $220 for 24,000 points (20,000 + 4000 [bonus]). Wyndham points convert at ratio of 2.5:1 to United Miles. Thus you would trade 24,000 Wyndham points to 9600 United Miles. Since United will give you 25% bonus on received miles which is 2400 additional miles (9600 x 25%). Thus you get 12,000 miles (9600 + 2400) for a payment of $220 which is ~1.833 cent/mile.
There is one more way of earning United Miles for same price as above if you do not mind renting a car at Alamo if it is available for cheap (This is YMMV and thus proceed with caution). For details of this promo offer which earns 1000 miles for 1 day rentals check here.
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