One of the most asked question and it was equally surprising for me that there was no direct result to this question when you do a google search.
So before we come to the Question “Why Oil Carriers can have a Greater Draft.” Let me remind you what is draft of a vessel – The draft or draught of a ship’s hull is the vertical distance between the waterline and the bottom of the hull (keel), with the thickness of the hull included; in the case of not being included the draft, outline would be obtained.
Teekay Shipping’s European Spirit suezmax oil tanker. (Teekay Shipping Ltd.)
https://www.ttnews.com/articles/ocean-shippers-fear-engine-failures-industry-forced-upgrade-fuel
You can see that oil tankers have a greater draft then bulk carrier, container ships etc. So let’s come to the reason why – Suppose the oil tanker somehow gets a hole below the waterline. Oil should leak now? But wait, Oil is less dense than water so the oil will remain on top of the water and since there is water everywhere outside the tank it will not sink easily. So we can have a greater draft in case of oil tankers.