Hi, I discovered the hard way that many options data at finance.yahoo.com are completely wrong! Below is an example screenshot of IONS. Also the options data for GUSH, CHK, FCEL, DRIP, GILD, RIG, AAPL, and many more are full of errors. Be careful with such "free" data! Especially when performance testing a system...
No one responded so let me give you my view. I found yahoo finance's options quotes generally correct but sometimes with delayed from the real time quotes. In any case if you trade options or stocks with a brokerage firm, their data is up to date and accurate. I don't think any of us use yahoo or google to trade or decide on trades.
Where is the error and how did it affect you? I use Yahoo Finance quotes on stocks and options to decide on option trades. I can sort of guess on the actual option price based on the Yahoo Finance 20-minute delayed option quotes and the Yahoo Finance 1-day live chart for the underlying - the final step is logging into my trading account and placing the trade.
For example the Ask price of strike 30 says $3.30, but in reality it is only $0.40. Similar with strikes 31, 33, 33.50, and 34. For me this is buggy data. Don't you think so?
In the previous posting I showed the error cases. It looks like that this buggy "free" data has cost me a friendship... B/c I had to drastically reduce my performance numbers of a system testing after testing it also with data from an other data source. The ex-buddy thinks it was my program's fault whereas it is the buggy data. Just one example: strike 30 has Bid=2.60 Ask=3.30 Last=2.50 But you never could short that strike (30) at that Bid price, or can you? Because the correct quotes are: Bid=0.00, Ask=0.40 ... For comparison, below is the correct data from finance.google.com :
Interesting comments. I use the data provided by my brokerage, real time, also pre, post market and historical for all my trading research, trades etc. and assumed other folks at ET would do the same. My apology to you and marsman.