Conversation so far:
Describe the Afra tanker scale.
AFRA uses a scale that classifies tanker vessels according to deadweight tons, a measure of a ship's capacity to carry cargo
Why was the Afra tanker scale developed?
The term is based on the Average Freight Rate Assessment (AFRA), a tanker rate system created in 1954 by Shell Oil to standardise shipping contract terms. Due to their favorable size, Aframax tankers can serve most ports in the world.
What are supertankers?
Supertankers are the largest tankers, and the largest man-made mobile structures. They include very large crude carriers (VLCC) and ULCCs with capacities over 250,000 DWT.
Describe supertankers' invention.
The first oil tankers were two sail-driven tankers that were built in 1863 on England's River Tyne. first ocean-going oil-tank steamer, the Vaderland, was designed and built by Palmers Shipbuilding and Iron Company of the United Kingdom for the American-Belgian Red Star Line in 1873,

Question: What are the important factors led to their development
Self-contained rewrite: What are the important factors led to supertankers' development?