It has the original side tank and the rear is a 1972 CJ5 tank plumbed through a transfer pump to the front tank. I asked for my special order frame to have a NAS rear tank mount but came with a TD5 rear tank mount so I rolled with it. The cj5 tank is almost a perfect fit in the rear tank cradle and cost around $75. The "sender" for a defender fuel tank fit right in. I planned to install a toggle switch that would switch the fuel gauge reading from front to back but I haven't gotten to it, and frankly haven't found that it would be all too necessary. When the front tank runs to about 1/8th tank I transfer the entire rear tank to the front then when I need a refill I fill both tanks. Range is around 650 miles when they are both full.