I am sure there are experts who can explain base oil pricing better.
From this link, it seems that Group II is may cost less than Group I base oil.
Group II+ 5-8% higher than Group II
Also, Group III appears about 21% higher than Group II.
So it seems that base oil price spread not as large as retail price spread of oil at the retail store. Group III base oil is more than 21% higher than group II at the store shelf unless there are many other factors that outweigh base stock prices.
If higher grade oils need less make up oil and additives than lower grade base oil, there should be less difference in price after additives are included. The oil bottles are often the same except for color and label for high and low base stock oils. Marketing and advertising varies widely.
http://www.imakenews.com/lng/e_article000645751.cfm?x=b11,0,w
From this link, it seems that Group II is may cost less than Group I base oil.
Group II+ 5-8% higher than Group II
Also, Group III appears about 21% higher than Group II.
So it seems that base oil price spread not as large as retail price spread of oil at the retail store. Group III base oil is more than 21% higher than group II at the store shelf unless there are many other factors that outweigh base stock prices.
If higher grade oils need less make up oil and additives than lower grade base oil, there should be less difference in price after additives are included. The oil bottles are often the same except for color and label for high and low base stock oils. Marketing and advertising varies widely.
http://www.imakenews.com/lng/e_article000645751.cfm?x=b11,0,w