The subject of many tourists, travelers and expats in Thailand seems to centre on what type of visa they have how they can extend their stay. Continuingly changing Thai policy certainly doesn't make the answers clear; embassy websites display the exact rules, but they can be confusing and don't always explain the cheapest and easiest ways to lengthen your stay.
There are several possibilities open to you depending on how long you want to stay.
If you are from any of the following countries you may enter the country with no preparation and will be given a visa for 30 days:
Australia, Austria, Belgium, Brazil, Bahrain, Brunei, Canada, Denmark, Finland, France, Germany, Greece, Hong Kong, Indonesia, Republic of Ireland, Israel, Italy, Japan, Republic of Korea, Kuwait, Luxembourg, Malaysia, Netherlands, New Zealand, Norway, Peru, Philippines, Portugal, Qatar, Singapore, Spain, South Africa, Sweden, Switzerland, Turkey, U.A.E, United Kingdom, United State of America, Vietnam.
You are allowed no more than 90 days in each 180 day period in the country (starting from the first time you entered the county on this visa). Therefore you can get two more of these after your first 30 day visit. You can do this by crossing a border out of the country and coming back in again. Visa run companies offer trips to cross the closest border to you (Malaysia, Burma, Laos or Cambodia). Depending upon where you are traveling from they can take up to a whole day and can be uncomfortable, but they are the cheapest way to renew your visa.
After you have had three of these in a row, you need to leave the country and get a tourist visa.
The closest countries where tourist visas can be obtained are Malaysia, Laos, Cambodia and Singapore. The details of the Thai embassies for these countries are listed below. Several budget airlines offer cheap flights to these destinations. You apply at the embassy for the visa, usually costing around $50 US. This will give you a 60 day stay, which can then be extended at a Thailand immigration office (found in all major Thai cities), for an extra 30 days (currently costing 1900 Baht. To do this and get the maximum out of your visa, you need to apply for the extension on the day the visa is due to expire.
After this set of 90 days expires you are then eligible for 3 more visas on arrival, or another Tourist visa from outside the country.
Other than marriage visas, work visas and educational visas there is another option.
The Royal Thai embassy in Hull England process 12 month quadruple entry tourist visas. You have to apply from the UK and enter the country within 3 months. The staff at the embassy are extremely helpful and have a remarkably fast turnaround time for this visa of 3 days. By leaving the country every 3 months the maximum stay of 12 months can be achieved. Details for the embassy are below.
The Thai Immigration office in Melbourne Australia can supply you with a 6 month double entry visa, each entry valid for 90 days. Again, they offer an excellent service with a very fast processing time (usually 24 hours).
Australia, Melbourne
566 St Kilda Rd
Melbourne, VIC 3004, Australia
Tel: +61 3 9533 9100
Fax: +61 3 9533 9200
Email: swallace@netspace.net.au
Cambodia, Phnom Penh
Royal Thai Embassy
No. 4 Boulevard
Monivong, Sangkat Srass Chork,
Khan Daun Penh, Phnom Penh
Tel :(85523) 426-182, 426-124
Fax: (85523) 810-860
Email: thaicompnh@bigponb.com.kh
Laos, Vientiane
(Lao People's Democratic Republic)
Royal Thai Embassy
Route Phongekheng,
Vientiane P.O. Box 128,
Tel: 214-582-3, 214-585-6
Fax: (66) 411-0017, (00785621) 214-580
Malaysia, Kula Lumpur
Royal Thai Embassy
206 Jalan Ampang,
50450 Kuala Lumpur
Tel : (03) 248-8222, 248-8350, 248-8420,245-8005
Fax : (03) 248-6527
E-Mail: thaikl@popl.jaring.my
Malaysia, Penang
Royal Thai Consulate-General
No. 1, Jalan Tunku Abdul Rahman
10350 Penang
Tel. (60-4) 2268029, 2269484
Fax:(60-4) 2263121
E-mail : thaipg@tm.net.my
Myanmar (Burma), Yangon
Royal Thai Embassy
45, Pyay Road, Yangon
Tel: +951 35 670, 33 082, 21 567
Fax: +951 22 784
Singapore
Royal Thai Embassy
370 Orchard Road
Singapore 238870
Tel: (65) 737-2444, 737-2158, 737-2175-6
Fax: (65) 732-0778
E-Mail: Thaisgp@singnet.com.sg
United Kindgom, Hull
James Bell House Connaught Rd,
Kingswood Hull HU7 3AQ,
United Kingdom
Tel: 01482 581668
Fax: 01482 580588
Website: thaiconsul-uk.com