Most Indie Campers campervans run on Diesel except for Rebel, Wrangler, Solis, and Solis Air which run on gasoline i.e. unleaded fuel. The tank fits 75-90 liters, depending on the size of the vehicle. The usage will vary on the driving behavior, but the average consumption is 8L for every 100km.
If you are renting a campervan, which is not part of the Indie Campers fleet, to make sure what is the capacity of the fuel tank please contact your host.