I have a Non-immigrant B Single-Entry 90 day Visa until the 17th of November and leaving Thailand officially on the 22nd of December. So my two questions are:

1. How can i make an extension to the visa until the end of my stay? What process do i need to follow?

2. I will probably be traveling during the 90 days, but since i have a single-entry, what do i have to do?

Welcome to the forum.

Have a look at this one http://www.thaivisa.com/forum/topic/484718-canhow-i-extend-my-non-immigrant-b-visa/

That thread has nothing to do with posters situation; which was a single entry visa. On entry you will receive a 90 day permitted to stay stamp so you must leave at the end of that time - as you have not say when you will arrive can not be sure if/what may be required.

1. No you can not extend more than 7 days to leave country unless you have work or other valid reason for such an extension - it does not appear that you will have any but without details of how/why you have the non immigrant B visa hard to advise.

2. You need a re-entry permit for any travel outside of Thailand to keep your permitted to stay 90 day alive for return - you use that as your return visa.

Expiration date of your visa has no meaning once you make entry - it is only that last day you can enter using that visa. If you arrive a few days before that date you would still have 90 day stay from day of arrival. If you need more time you can exit/return at a land border for 15 days (if from a normal visa exempt country) or 30 days by air or leave and obtain a tourist visa for 60 day stay at a Consulate in a bordering country. That will require an overnight stay most places but up to 4 days in Cambodia.

I got a B Non-Immigrant Visa due to me working in Bangkok.

I entered Thailand with the 90 days on August 25th. So i have 90 days from that date?

Yes 90 days with day of entry August 25 being day one. Be aware you can not work without a work permit and for work permit to be valid you must be here on a non immigrant visa entry.

So in order to stay that extra month that i need, i would have to leave Thailand, and then when i enter i would get the 30 days extension?

No you would have to exit to obtain a new non immigrant B visa and return on that if intending to work.

So i would have to leave for more than a weekend then?

Yes as Consulates are not open on weekends and normal is apply in morning and pick up next workday afternoon at most places. Extensions of stay are available from Immigration for valid reasons as outlined in police order 777/2551 (Google will find) but this requires a bit/lot of paperwork and expect your employer would have mentioned if your employment qualified.

Hi,

My B visa is valid until 5.9., but I visited Poi pet on 19.8., applied for Cambodian and now this visa expires 3.9.. Am I allowed to stay in Thailand until 5th or 3rd?

You no longer have a non-B visa. it seems that when you left Thailand you didn't had a re-entry permit and got a 15 day visa exempt entry, on which you cannot work.

You can stay till 3 Sept.

Do I have to make another Cambodian visa, since it is single entry, but is still valid?

You appear to have had a single entry non immigrant B visa entry valid for a stay until 5 Sep but did not obtain a re-entry permit so when you returned from Cambodia were stamped for a 15 day visa exempt entry and must leave by 3 Sep.

Do I have to make another Cambodian visa, since it is single entry, but is still valid?

Single entry is just that. 1 entry into Thailand, which you already had.

There is no such thing as stupid Q, so here it goes:

Is my Cambodia still valid although it is stamped USED... since date is still valid... umph!?

Read the post above your last one.

The Cambodian visa for entry to Cambodia was used, therefore it is no longer valid.