Before one goes to Vientiane I suggest you read what one of our Admin says :
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Vientianne:
Suitable for apply Non B (only one in one full year),
Non ED (most first timers have no problem, only one application from Language Schools in one full year , cover letter must only indicate your specific level & show bank balance THB 20,000.-. As of now we can not confirm on how to do with second year applicants).
OK for Non O Single Entry if married to Thai or support Thai Child (if back to back application, they will ask show money THB 200,000.- in Thai Bank Account).
For application Non O Volunteer first time OK(if back to back need guarantee letter from said Ministry equivalent to department level).
Tourist Visa, if you had previously some Tourist visas your application will be considered more carefully. Vientiane is now, in most cases, asking for proof of funds, Book Bank with balance THB 20,000.- up OR print out from Bank account from home country value USD 700.-up. Onward air ticket is not required.