The big issue for travelling to Thailand without a visa is the need for Proof of Onward Travel as called for in the rules on visa exemptions. This is checked by the AIR CARRIERS at check-in and they require a confirmed flight out of Thailand within the 30-day period of stay, otherwise they could deny you boarding. Plans for overland transportation do not count. Carriers in Europe, North America and Australia are particularly strict about this, fearing fines and being forced to transport you back without payment. Regional airlines are usually lax on this, and Thai Immigration hardly ever checks. Solutions: get a flight on a low-cost carrier out of Thailand within the 30 days even if you don’t intend to use it, or get a tourist visa in advance. (The 30-day exemption is not any kind of visa.)

@Pat****

the bus starts at Dongphosy train station on Lao territory. You have to cross the border on your own.

OK maybe it does, but it still probably wouldn’t work for Proof of Onward Travel because it’s not verifiable.

@Patrick *********

Does it really? My impression was that it takes you to the Friendship Bridge, then you have to cross the bridge and, once in Laos, buy a ticket for a bus to Vientiane. Please correct me if I’m wrong.

But even so, this would not remove the need for a verifiable flight, and your fate would be in the hands of a check-in agent who may not be feeling generous that day.

@Robert ******

The airline check-in agents want to see a confimed FLIGHT which they can check on their IATA database. A bus ticket will not do – in fact AFAIK most bus tickets available in advance do not cross borders anyway. The OP should buy a cheap flight to Laos instead of traveling by land. Problem solved.

@Ci***

there is no transit visa available at any Thai airport. Period. Thailand does have a transit visa but it has to be obtained in advance and it’s really only applicable for those not eligible for visa exemption or Visa on Arrival or ship’s crew members. Just use your 30-day visa exemption. There is no downside to that.

@Emmanuel *******

As long as you have a confirmed air ticket out of the country within the 30 days, you're meeting the letter of the law. That's all they care about. Look for the cheapest Air Asia ticket. I think Bangkok to Penang is always the lowest cost.

@Amaël *****

You might not even be aware they're checking it. The airline check-in software automatically accesses the Timatic database to check for visa compliance and returns "OK" or "Visa Required." The agent leafs through the passport to find your visa, if needed. That's it. I once had to convince an Air Berlin check-in agent that February had 28 days.

What’s important is whether you booked this on ONE TICKET with one PNR or you have two separate tickets. If it’s all booked on one ticket your luggage will be checked through to destination, you will be a CIQ passenger in transit and you’ll pass through a special security line and go to your gate. If it’s two separate tickets, you will have to clear Immigration in oder to claim your luggage, check in again and go through outgoing passport control and security. If you are a Cambodian national, you’re eligible for a free 14-day visa exemption, so you do not require a visa.

I’m afraid this goes way beyond my level of expertise which is purely focused on tourist visas.