Why does Yahoo Finance and Google Finance not match historical prices?
The difference is that Yahoo is showing the unadjusted price that the security traded for on that date, while google is adjusting for price splits. This means that Google is showing how much you would have had to pay to get what is now one share. Since 1979, JNJ has split 3-for-1 once, and 2-for-1 four times. 3x2x2x2x2 = 48. If you bought 1 share at that time, you would now have 48 shares today. Yahoo is showing a price of $66 for what was then 1 share. $66/48 = 1.375, which Google rounds to 1.38. You can see this if you get the prices from May 14-21, 1981. The stock split 3-for-1, and the price dropped from 108 to 36.38. Yahoo's adjusted close column has not been accurate since they re-wrote the Finance website. It now just represents the closing price. The other relevant field on Yahoo is the Adj. Close. This adjusts for splits, but also adjusts for dividends. Hence why this doesn't match either the Google or Yahoo numbers. I work on a buy-side firm, so I know how these small data issues can drive us crazy. Hope my answer below can help you:  Reason for price difference: 1. Vendor and data source Basically, data providers such as Google and Yahoo redistribute EOD data by aggregating data from their vendors. Although the raw data is taken from the same exchanges, different vendors tend to collect them through different trading platforms. For example, Yahoo, is getting stock data from Hemscott (which was acquired by Morningstar), which is not the most accurate source of EOD stocks. Google gets data from Deutsche Börse.  To make the process more complicated, each vendor can choose to get EOD data from another EOD data provider or the exchange itself, or they can produce their own open, high, low, close and volume from the actual trade tick-data, and these data may come from any exchanges.  2. Price Adjustment  For equities data, the re-distributor usually adjusts the raw data by applying certain customized procedures. This includes adjustment for corporate actions, such as dividends and splits. For futures data, rolling is required, and back-ward and for-warding rolling can be chosen. Different adjustment methods can lead to different price display.  3. Extended trading hours  Along with the growth of electronic trading, many market tends to trade during extended hours, such as pre-open and post-close trading periods. Futures and FX markets even trade around the clock. This leads to another freedom in price reporting: whether to include the price movement during the extended trading hours.   Conclusion To cross-verify the true price, we should always check the price from the Exchange where the asset is actually traded. Given the convenience of getting EOD data nowadays, this task should be easy to achieve.  In fact, for professional traders and investors alike, they will never reply price on free providers such as Yahoo and Google, they will most likely choose Bloomberg, Reuters, etc. However, for personal use, Yahoo and Google should both be good choices, and the difference is small enough to ignore.
"I'm familiar with and have traded U.S.-listed LEAPS and I've always used the CBOE quotes page you linked to.  So, I too was surprised I couldn't find 3M (MMM) LEAPS quotes at that page, even after checking the ""List all options, LEAPS, Credit Options & Weeklys if avail."" radio button.  Used to work! Fortunately, I was able to get access to the full chain of option quotes from the CBOE's other quotes page:  Go to the ""Quotes & Data"" menu, then select Delayed Quotes - NEW!  Here's how: I think the new interface is terrible: it's too many steps to get to the information desired.  I preferred the all-in-one table of the Delayed Quotes Classic page, the one you linked to. As to why that classic page isn't yielding the full chain, I can only suggest it is a recently introduced bug (software defect).  I certainly was able to get LEAPS quotes from that page before. On Yahoo! Finance option quotes: I don't know why their chain is incomplete – I can't see the logic, for instance, as to why MMM Jan 2012 60 calls are missing.  I thought at first it may be lack of volume or open interest, but nope.  Anyway, I don't trust Yahoo! to provide accurate, reliable quotes anyway, having seen too many errors and missing data in particular in the feed of Canadian stocks, which I also trade. I rely on the exchange's quotes, and my broker's real-time quotes.  I check Yahoo! only for convenience sake, and when it actually matters I go to the other more reliable sources. For what it's worth, though, you can also get full chain option quotes at NASDAQ.  See here for the 3M (MMM) example then click on the ""Jan 12"" link near the top.  However, I would consider CBOE's quotes more definitive, since they are the options exchange." "Matt explains the study numbers in his answer, but those are the valuation of the brand, not the value of the company or how ""rich"" the company is.   Presuming that you're asking the value of the company, the usual way for a publicly traded company to be valued is by the market capitalization (1).  Market capitalization is a fairly simple measure, basically the total value of all the shares of stock in that company. You can find the market cap for any publicly traded company on any of the usual finance sites like Google Finance or Yahoo Finance. If by rich you mean the total value of assets (assets being all property, including cash, real property, equipment, and licenses) a company owns, that information is included in a publicly traded company's quarterly SEC filing and investor releases, but isn't usually listed on the popular finance sites. An example can be seen at Duke Energy's Investor Relation Site (the same information can be found for all companies on EDGAR, the SEC's search tool).  If you open the most recent 8-K (quarterly filing), and go to page 8, you can see that they have $33B+ in assets, and a high level breakdown of those. Note that the numbers are given in millions of dollars For a privately held company this information may or may not be available and you'd have to track it down if it is available. I picked Duke Energy because it's the first thing that popped into my mind.  I have no affiliation with Duke, and I don't directly own any of their stock." Yahoo finance does in fact have futures quotes.  But I've found them difficult to search for because you also have to know the expiration codes for the contract to find them. S&P 500 Emini quote for June 2012 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. I agree that a random page on the internet is not always a good source, but at the same time I will use Google or Yahoo Finance to look up US/EU equities, even though those sites are not authoritative and offer zero guarantees as to the accuracy of their data. In the same vein you could try a website devoted to warrants in your market.  For example, I Googled toronto stock exchange warrants and the very first link took me to a site with all the information you mentioned.  The authoritative source for the information would be the listing exchange, but I've spent five minutes on the TSX website and couldn't find even a fraction of the information about that warrant that I found on the non-authoritative site. To quote their disclaimer: Data is provided by financial exchanges and may be delayed as specified by financial exchanges or our data providers. Google does not verify any data and disclaims any obligation to do so. That means that they buy it from a reseller such as IDC. It probably differs in source between the different exchanges depending on price and availability factors. They do specify in some cases which reseller they use and one of those happens to be Interactive Data (IDC) who are also the data provider used in my day job! "In the US, stocks are listed on one exchange but can be traded on multiple venues.  You need to confirm exactly what your data is showing: a) trades on the primary-listed exchange; or b) trades made at any venue. Also, the trade condition codes are important.  Only certain trade condition codes contribute towards the day's open/high/low/close and some others only contribute towards the volume data.  The Consolidated Tape Association is very clear on which trades should contribute towards each value - but some vendors have their own interpretation (or just simply an erroneous interpretation of the specifications). It may surprise you to find that the majority of trading volume for many stocks is not on their primary-listed exchange.  For example, on 2 Mar 2015, NASDAQ:AAPL traded a total volume across all venues was 48096663 shares but trading on NASDAQ itself was 12050277 shares. Trades can be cancelled.  Some data vendors do not modify their data to reflect these busted trades.   Some data vendors also ""snapshot"" their feed at a particular point in time of the data.  Some exchanges can provide data (mainly corrections) 4-5 hours after the closing bell.  By snapshotting the data too early and throwing away any subsequent data is a typical cause of data discrepancies.   Some data vendors also round prices/volumes - but stocks don't just trade to two decimal places. So you may well be comparing two different sets of trades (with their own specific inclusion rules) against the same stock.  You need to confirm with your data sources exactly how they do things. Disclosure: Premium Data is an end-of-day daily data vendor." You might have better luck using Quandl as a source.  They have free databases, you just need to register to access them.  They also have good api's, easier to use than the yahoo api's Their WIKI database of stock prices is curated and things like this are fixed (www.quandl.com/WIKI ), but I'm not sure that covers the London stock exchange.  They do, however, have other databases that cover the London stock exchange.