From the Thaiger

Starting next month, bus travel enthusiasts in Thailand will have 10 bus route options options in Laos. One of the Thailand-Laos bus routes began earlier this month, from Mukdahan to Savannakhet. Now, the president of Transport Co Ltd, Sanyalux Panwattanalikit, has listed 9 new Thailand-Laos routes starting June 15.

The new routes will be: Nong Khai to Vientiane, Udon Thani to Vientiane, Ubon Ratchathani to Pakse, Khon Kaen to Vientiane, Bangkok to Vientiane, Nakhon Phanom to Thakhek, Chiang Rai to Bokeo, Loei to Luang Prabang, and a line running between Udon Thani, Udon Thani International Airport, Nong Khai, and Vang Vieng.

To buy tickets for busses from Thailand to Laos, travel nerds can visit https://tcl99web.transport.co.th/Home.

I've never had much of a problem crossing Laos to Thai borders.

Last time I went to Vientiane,  I missed the train from Udon Thani to Nong Khai, thanks to inaccurate "live" train scheduling information from Thai railways.    I walked up the road and got a minivan for 50 baht, which dropped me off at the border.    After crossing the border, I just hopped on a local bus the other side.      The first time, I just walked out of Udon Thani Airport and almost immediately caught a minivan to the border.   

A few years ago, I exited Laos at Hua Xai border post, crossed the river on a boat barely bigger than a canoe and was swiftly stamped into Thailand on the other side.    Just up the road, there were minivans running to Chiang Mai and Chiang Rai.     I suspect it might be slightly more difficult, now there is a bridge north of the town.

Exiting Pakse a couple of years ago, it did take me about an hour to find a mini bus to the border, which is not ideal.   Finding a bus from the border to Ubon Rachathani was quite easy.   

Perhaps the website will make life easier, but it is a typical clunky Thai website.   I tried searching Pakse.  That appears twice, once with no destinations and once with destinations including Chong Mek (the  border) and "Ubol Rachathani".   Selecting for late June, it doesn't yet show any bus schedules.      I'll bookmark it for reference on future trips.