There are several ways of acquiring a vehicle. Depending on your starting planet you should receive the basic form of transportation by doing the beginner quests. If you want to have a more advanced vehicle you can buy one from other players either via the auction or direct trade.
There are a large variety of vehicles in the Entropia Universe, and you can find one for any situation. There are vehicles for traveling on the ground, over water, through the air and even between planets in space.
This is most likely because it is not possible to sell a vehicle that still has oil in it. Please extract the oil and then try selling the vehicle again. If you are still experiencing difficulties after this then please contact Support by sending in a case.
This can sometimes happen when you just started playing and the client has not fully been downloaded. The vehicle can be retrieved from your storage. If you can't find it in your storage we suggest that you restart the client by relogging.
Whenever you log out, if you have a spawned vehicle, it will automatically be sent to your storage after a short period of time. The same happens if your vehicle gets out of your radar zone for a while.
Also sometimes vehicles get placed at the very bottom of the inventory window, try to scroll down to the bottom to see if your vehicle is there.