Are volatilities for equity options quoted in the market on a stock by stock basis or are only index volatilities quoted and the volatility of an individual stock must be backed out via some correlation model?In other words, for FX or IR, volatility is limited to a currency pair or a currency (forward rate, swap rate, exchange rate, etc). But for stocks, there are unlimited amount of companies to track. Motivation: If someone was writing software that allowed a user to input equity volatility, should the volatility be on a stock by stock basis or more general?I guess really what I am asking for is in data feeds like bloomberg, what is the mechanism by which you extract the volatility for a specific equity option to plug into B-S formula? thanks-Sean

for listed equity options assume one vol per ticker, strike and maturity. for anything more complicated... it's a long story...

That makes sense...but what about the unlisted options (like perhaps some small cap stocks)care to elaborate :-0 (or point me to a paper/textbook/web source)?PS I dont care about exotics, just illiquid vanilla optionsthanks for your time

"I guess really what I am asking for is in data feeds like bloomberg, what is the mechanism by which you extract the volatility for a specific equity option to plug into B-S formula? "For each stock Bloomberg will have historical vol (I think its over the past 100 days).

bloomberg lists 10, 50, 100 and 200 days historical volatilities.what you put into B-S is another story too...each ticker with listed options, of which - each maturity, call and put, and strikes may have different volas. Hence the volatility surface(s).