Well, I dont think you will have tankers with 48000/56000 liters capacity. They would be too large.
Here in India normal tanker has three compartments with a capacity of 4000 ltrs for each. Some larger ones have capacity of 16000 liters.
Also consider a 48000 liters capacity tank will have laden waight of about 46.5 tonnes and would require a very large and powerful truck to pull it.
This is 16000 liters tanker.