I know that American Express Platinum or Citibank offer earning rates of 1 mile / 20-25 Baht spent, but for those of us on sub-80K salaries, I reckon UOB offers an interesting option via their savings account + Visa Electron card:

-1 mile / 50 Baht spent using the card

-50K initial deposit required for setting up the savings account (but immediately withdrawable if you need it)

-needs a work permit, but nothing else (no salary limits or taxation proofs)

-sends a statement to your house every month detailing all spending and points accrued (just like a regular CC)

Also, they have decent customer service, in my opinion...and being an international bank, it raises fewer eyebrows internationally then trying to pay with a "We Love the King" Bangkok Bank card

I've had a UOB card for a couple of years, and have raked up about 50K miles on it. Not as 'efficient' as the CC, but it is free. I also thought it was one mile for 25 baht, not 50. Ah well, you learn something new everyday!

Actually, you get one UOB Reward Point for 20 Baht, but 1 ROP mile = 2.5 UOB points, so yeah, 50 Baht/mile.