Buy at least 40,000 miles at USD$0.0275 each and get 50% bonus miles.
If you are into the miles game, you will know that Alaska Mileage Plan is kind of a stray horse here that gives incredibly good value. They also run regular promotions that gives bonus miles when you buy miles from them.
The promotion

From now until 19 May 2019 11.59pm Pacific Standard Time, which is 20 May 2019 2.59pm Singapore Time, earn between 20 to 50% bonus miles when you buy miles. The bonuses go up when you buy more miles:
- Under 10,000 miles – no bonus
- 10,000 to 19,000 miles – 20% bonus
- 20,000 to 39,000 miles – 35% bonus
- 40,000 to 60,000 miles – 50% bonus
If you want to buy more than 60,000 miles, you will need to make a new transaction. Note that Alaska Mileage Plan limits members to a maximum of 150,000 miles bought each year (this includes bonus miles), unless you hold status with the programme.
What are they good for?
For the uninitiated, Alaska Air has amassed quite a good portfolio of partners to earn and redeem miles on, including Japan Airlines (JAL), Cathay Pacific, Emirates and more.
One of the most widely known sweet spot with this programme is the ability to book a quasi-return trip on JAL in business class for only 25,000 miles.
How to book the ‘return’ trip on Japan Airlines:
Japan Airlines (JAL) charges only 25,000 miles for intra-Asia itineraries involving a maximum of 1 stop, to count it as a ‘one-way’ journey. Alaska Air also allows for a stopover, i.e. staying in the intermediate point for more than 24 hours.
Using the rule above, you can technically book something like, Bangkok to Singapore via Tokyo on JAL business class, which will only cost you 25,000 miles because it is technically a one-way itinerary. All you need to do is to buy another (cheaper) ticket to Bangkok to start your journey.
Another sweet spot is that JAL allows for open-jaw booking, so you can booking something like Bangkok-Osaka, then Tokyo-Singapore in a same journey.

Singapore Airlines have also joined them as a partner, but the partnership is limited to earning Alaska Mileage Plan miles for now. Redemption will be made available at a later date.
Good mileage programme to credit miles
I’ve credited a couple of my Qantas trips with Alaska Mileage Plan before and found it incredibly good value: Business class trips get up to 225% of the actual mileage flown.
For instance, I credited a one-way business class flight from Sydney to Singapore last year, and for the actual 3,912 miles flown, I got 8,802 miles credited after factoring in the bonuses.

If you ever buy a revenue ticket with Emirates in business or first class, be sure to credit that in with Alaska Mileage Plan as well for hefty bonuses.

This may be sacrilegious to some, but you can also credit your Singapore Airlines mileage to Alaska Mileage Plan as well. In business class, you can earn up to 225% of the mileage flown, so if you fly the Singapore-Newark non-stop service in business, you can earn up to 21,431 miles!