I agree with Viking. My husband is a cognac drinker.
The difference between VS(very special), VSOP(Very Superior
Old Pale) & XO cognac are the years & of course it cost. VS are at least 2 1/2 - 4 1/2 yrs old, VSOP are at least 4 1/2 -6 1/2 yrs old & XO(extra old) at least 6 1/2 years or much much older which would cost a lot of money some would even cost thousands of dollars then there is a LOUIE xiii which of course much more expensive than the rest.
Most common cognac are Hennesy, martell, courvoisier. My husband still kep that bottle of cognac that was given to him as a gift the Camus cognac XO superior. Lol
Check
http://www.cognac.com