A frame structure serves to accommodate a plurality of non-standardized small tanks or containers to form a transport unit of standard overall dimensions. The small containers are of the type having foot portions formed with channels or openings for receiving fork lift arms. The frame structure includes a bottom group with a plurality of parallel struts extending in one direction and a number of further frame members extending in the other direction. These struts and frame members form windows for receiving the foot portions of the small containers. Locking members are provided which engage the channels formed in the foot portions of the small containers for coupling these to the frame structure.