Comparing option data between yahoo finance and CBOE for SPY options
The CBOE site, as well as some other sites and trading platforms, will show the bid/ask and statistics for that option at each individual options exchange, in addition to statistics and the best bid/offer across all exchanges. cboe.com: Delayed Quote Help lists what the single-letter codes mean. A is for the AMEX options exchange, B is for BOX, X is for PHLX, etc.
Many exchanges trade the same securities.  An order may be posted to a secondary exchange, but if the National Best Bid and Offer data provider malfunctions, only those with data feeds from that exchange will see it. Only the data provider for the primary exchange where a stock is listed provides the NBBO. Missing orders are very common with the NBBO data providers.  NASDAQ's order consolidator has had many failures over the past few years, and the data provider's top executive has recently resigned. Brokers have no control over this system.  A broker may be alerted to a malfunction by an accountholder, but a broker may only inform the relevant exchange and the relevant data provider. There are several Excel spreadsheets for downloading stock quotes (from Yahoo Finance), and historical exchange rates at http://investexcel.net/financial-web-services-kb Robert Shiller has an on-line page with links to download some historical data that may be what you want here. Center for the Research in Security Prices would be my suggestion for another resource here. Options - yes we can :) Options tickers on Yahoo! Finance will be displayed as per new options   symbology announced by OCC. The basic parts of new option symbol are: Root symbol + Expiration   Year(yy)+ Expiration Month(mm)+ Expiration Day(dd) + Call/Put   Indicator (C or P) + Strike price Ex.: AAPL January 19 2013, Put 615 would be AAPL130119P00615000 http://finance.yahoo.com/q?s=AAPL130119P00615000&ql=1 Futures - yes as well (: Ex.: 6A.M12.E would be 6AM12.CME using Yahoo Finance symbology. (simple as that, try it out) Get your major futures symbols from here: http://quotes.ino.com/exchanges/exchange.html?e=CME "http://www.interactivedata.com -&gt; reference data  No, it's not free. Nor would I consider it ""high quality"".  For free data, try the Yahoo Finance API.  The data you want is there, though you may need to calculate some of the fields yourself.  Once you have your application working with free data you will be in a good position to evaluate whether it's worth it to shift to more detailed non-free data." "BestInvest is a UK site looking at that URL, base on the ""co.uk"" ending. Yahoo! Finance that you use is a US-based site unless you add something else to the URL. UK & Ireland Yahoo! Finance is different from where you were as there is something to be said for where are you looking. If I was looking for a quarter dollar there are Canadian and American coins that meet this so there is something to be said for a higher level of categorization being done. ""EUN.L"" would likely denote the ""London"" exchange as tickers are exchange-specific you do realize, right?" you can try CME DataSuite. Your broker gives you real time options quotes. If you do not have one you can open a scottrade account with just $500 deposit. When I moved my money from scottrade to ameritrade they did not close my account even till this day I can access my scottrade account and see real time quotes and the same research they offered me before. You can try withdrawing your deposit and see if it stays open like mine did. You may refer to project http://jstock.sourceforge.net. It is open source and released under GPL. It is fetching data from Yahoo! Finance, include delayed current price and historical price. "Interactive Brokers offers global securities trading. Notice that the security types are: cash, stock (STK), futures (FUT), options (OPT), futures options   (FOP), warrants (WAR), bonds, contracts for differences (CFD), or   Dutch warrants (IOPT) There is a distinction between options (OPT), warrants (WAR), options on futures (FOP) and finally, Dutch Warrants (IOPT). IOPT is intuitively similar to an ""index option"". (For index option valuation equations, iopt=1 for a call, and iopt= -1 for a put. I don't know if Interactive Brokers uses that convention).  What is the difference between a ""Dutch Warrant"" and an option or warrant? Dutch warrants aren't analogous to Dutch auctions e.g. in the U.S.Treasury bond market. For North America, Interactive Brokers only lists commissions for traditional warrants and options, that is, warrants and options that have a single stock as the underlying security. For Asia and Europe, Interactive Brokers lists both the  ""regular"" options (and warrants) as well as ""equity index options"", see commission schedule. Dutch warrants are actually more like options than warrants, and that may be why Interactive Brokers refers to them as IOPTS (index options). Here's some background from a research article about Dutch warrants (which was NOT easy to find): In the Netherlands, ING Bank introduced call and put warrants on the   FT-SE 100, the CAC 40 and the German DAX indexes. These are some differences between [Dutch] index warrants and exchange traded index options: That last point is the most important, as it makes the pricing and valuation less subject to arbitrage. Last part of the question: Where do you find Structured Products on Interactive Brokers website? Look on the Products page (rather than the Commissions page, which does't mention Structured Products at all). There is a Structured Products tab with details." As another answer started, this information comes straight from an exchange and generally costs a fortune . . . However things change: IEX, a new exchange, recently opened and they are offering real time bid/ask data for free. Here's the API description: https://www.iextrading.com/developer/ This data should be good for active securities, but for securities less actively traded the numbers might be stale. For self-service type online customers, OptionsXpress gives me far better trading features(like technicals advanced conditions) and tools, ACH money management & scheduling, fullfillment too. $9 stock trades.  I don't know if they yet share Schwab's (their new parent company?) commission-free ETFs getting so trendy nowadays. "I'm assuming the question is about how to compare two ETFs that track the same index. I'd look at (for ETFs -- ignoring index funds): So, for example you might compare SPY vs IVV: SPY has about 100x the volume. Sure, IVV has 2M shares trading, so it is liquid ""enough"". But the bigger volume on SPY might matter to you if you use options: open interest is as much as 1000x more on SPY. Even if you have no interest in options, the spreads on SPY are probably going to be slightly smaller. They both have 0.09% expense ratios. When I looked on 2010-9-6, SPY was trading at a slight discount, IVV was at a slight premium. Looking for any sort of trend is left as an exercise to the reader... Grab the prospectus for each to examine the rules they set for fund makeup. Both come from well-known issuers and have a decent history. (Rather than crazy Uncle Ed's pawn shop, or the Central Bank of Stilumunistan.) So unless you find something in the SPY prospectus that makes you queasy, the higher volume and equal expense ratios would seem to suggest it over IVV. The fact that it is at a (tiny) discount right now is a (tiny) bonus." Google Finance and Yahoo Finance have been transitioning their API (data interface) over the last 3 months. They are currently unreliable. If you're just interested in historical price data, I would recommend either Quandl or Tiingo (I am not affiliated with either, but I use them as data sources). Both have the same historical data (open, close, high, low, dividends, etc.) on a daily closing for thousands of Ticker symbols. Each service requires you to register and get a unique token. For basic historical data, there is no charge. I've been using both for many months and the data quality has been excellent and API (at least for python) is very easy! If you have an inclination for python software development, you can read about the drama with Google and Yahoo finance at the pandas-datareader group at https://github.com/pydata/pandas-datareader. Try Google Finance Screener ; you will be able to filter for NASDAQ and NYSE exchanges. I don't see it in any of the exchange feeds I've gone through, including the SIPs. Not sure if there's something wrong with Nasdaq Last Sale (I don't have that feed) but it should be putting out the exact same data as ITCH.