Fuel on the Pakse - Chong Mek road
There are no internationally-branded fuel stations on the road between Pakse in Laos and the Laos/Thai border. There is only a small "local" fuel outlet at the junction on this road to Champasak.
If you wish to take advantage of the cheaper (than Thailand) Laotian fuel, or just want to get rid of your non-exchangeable Laos Kip before leaving the country, fuel up in Pakse.
Note that the bridge over the Mekong is a toll affair. For my 6-wheels, it cost 10,000kip. So leave at least this amount in your wallet after tanking up.