If you enter Thailand via land border, you will be stamped a 15-day permission of stay as a tourist in the immigration post, after which you will have to exit the country again on or before the expiration of your permission of stay. However, the tourist visa can also be extended if you wish or need to stay longer in Thailand. You will have to file an application for an extension of stay at the Office of Immigration Bureau located at Soi Suan Plu, off South Sathorn Road, Bangkok 10120 , Tel (662) 287-3101-10. Bear in mind that the success for an extension of stay is solely at the discretion of the immigration officer attending on your application.