Stock exchanges open on Saturday
According to Wikipedia as well as this stock market trading-hours website, the Tehran Stock Exchange is open Saturday through Wednesday.
A stock's price does not move in a completely continuous fashion.  It moves in discrete steps depending on who is buying/selling at given prices. I'm guessing that by opening bell the price for buying/selling a particular stock has changed based on information obtained overnight. A company's stock closes at $40.  Overnight, news breaks that the company's top selling product has a massive defect.  The next morning the market opens.  Are there any buyers of the stock at $40?  Probably not.  The first trade of the stock takes place at $30 and is thus, not the same as the previous day's close. You need a source of delisted historical data.  Such data is typically only available from paid sources. According to my records 20 Feb 2006 was not a trading day - it was Preisdent's Day and the US exchanges were closed. The prior trading date to this was 17 Feb 2006 where the stock had the following data: Open: 14.40 High 14.46 Low 14.16 Close 14.32 Volume 1339800 (consolidated volume) Source: Symbol NVE-201312 within Premium Data US delisted stocks historical data set available from http://www.premiumdata.net/products/premiumdata/ushistorical.php Disclosure: I am a co-owner of Norgate / Premium Data. Why do you care? In any case, you can easily Google the answer... Effective Sunday, April 2, 2017 for trade date Monday, April 3, 2017, and pending all relevant CFTC   regulatory review periods, Chicago Mercantile Exchange Inc. (“CME” or “Exchange”) will list Monday   Weekly Options on the E-mini Standard and Poor’s Stock Price Index Futures and Standard and Poor’s   500 Stock Price Index Futures contracts (collectively the “Contracts”) for trading on CME Globex and for   submission for clearing via CME ClearPort as described in Appendix A below. Appendix B below provides   the Exchange fee schedule for the Contracts. source I've never seen a dividend, split or other corporate action during the day, but I have seen trade suspended a few times when something big happened. The market opening price is not in general the same as the close of the previous day. It can gap up or down and does frequently. I don't know of an api to find out if the dividend was cash or stock, but stock dividends are a lot less common. If a company's shares trade in multiple exchanges, the prices in every exchange are very near to each other, otherwise you could earn money by doing arbitrage deals (buying in one, selling in the other) - and people do that once it becomes worth it. Which stock exchange you use is more a convenience for the buyer/seller - many investment banks offer only something local/near, and you have to go to specific investment banks to use other exchanges. For example, in Germany, it is easy to deal in Frankfurt, but if you want to trade at the the NASDAQ, you have to run around and find a bank that offers it, and you probably have to pay extra for it. In the USA, most investment banks offer NASDAQ, but if you want to trade in Frankfurt, you will have run around for an international company that offers that. As a stock owner/buyer, you can sell/buy your shares on any stock exchange where the company is listed (again, assuming your investment broker supports it). So you can buy in Frankfurt and sell in Tokyo seconds later, as nothing needs to be physically moved. Companies that are listed in multiple stock exchangs are typically large, and offer this to make trading their shares easier for a larger part of the world. Considering your 'theoretical buy all shares' - the shares are not located in the exchanges, they are in the hands of the owners, and not all are for sale, for various reasons. The owners decide if and when they want them offered for sale, and they also decide which stock exchange they offer them on; so you would need to go to all exchanges to buy them all. However, if you raise your offer price in one exchange only slightly, someone will see the arbitrage and buy them in the other locations and offer them to you in your stock exchange; in other words, for a small fee the shares will come to you. But again, most shares are typically not for sale. It's the same as trying to buy all Chevy Tahoes - even if you had the money, most owners wouldn't know or care about you. You would have to go around and contact every single one and convince them to sell. "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." "As someone that works in and with the ag and commodity markets, my understanding, is limited but I hope it helps.   Aside from needing an infrastructure built to maintain the vast amounts of data, communication, pricing, banking information, having a closing time for our markets helps to ensure value and fair trade. Capitalism is centralized around creating a fair value for ventures to sell, where prospective buyers opt to purchase or invest. For example, where I attended university, there were many coffee shops close to campus, but only one stayed open all night, and as such had operational cost much higher than other shops, forcing them to charge more for a cup of coffee. While this example is crude, the idea is the same. By maintaining""bank"" hours, product or strategies and developments meant to increase projected value are allowed to occur.   I imagine that if the markets did not close, my coffee prices would skyrocket for an increased demand, that of which the supply chsin, and farmers, would struggle to meet. The same would be said of grain, salt, oils, etcetera." There are several reasons why this may happen and I will update as I get more information from you. Volumes on that stock look low (supposing that they are either in a factor between 1s and 1000s) so it could well be that there was no volume on that day. If no trades occur then open, high and low are meaningless as they are statistics based on trades that occur that day and no trades occur. Remember that there has to be volume to get a price. The stock may have been frozen by either the exchange or the company for the day. This could be for various reasons including to prevent some illegal activity. In that case no trades were made because the market for that stock was closed. Another possibility is that all trades that day were cancelled by the exchange. The exchange may cancel all trades if there is unusual, potentially fraudulent or other illegal activity on the stock. In this case the last price for that day existed but was rolled back by the exchange and never occurred. This is a rare situation. Although I can't find any holidays on that date it is possible that this is how your data provider marks market holidays. It would be valid to ignore the data in that case as being from a non-market day. I cannot tell if this is possible without knowing exchange information. There is a possibility that some data providers don't receive data for a day or that it gets corrupted. It may be worth checking another source to ensure the integrity of the data that you are receiving. Whichever reason is true, the data provider has made the close equal to the previous day's close as no price movements occurred. Strictly the closing price is the price of the last trade made for that day and so should be null (and open, high and low should be null too and not 0 otherwise the price change on day is very large!). Therefore, to keep integrity, you have a few choices: The NYSE holidays are listed online here: https://www.nyse.com/markets/hours-calendars "Company values (and thus stock prices) rely on a much larger time frame than ""a weekend"".  First, markets are not efficient enough to know what a companies sales were over the past 2-3 days (many companies do not even know that for several weeks).  They look at performance over quarters and years to determine the ""value"" of a company.  They also look forward, not backwards to determine value.  Prior performance only gives a hint of what future performance may be.  If a company shut its doors over a weekend and did no sales, it still would have value based on its future ability to earn profits." "listed simultaneously in New York, London, and maybe even some Asian markets - is this correct? If the exchanges are not connected, then in primary market the shares are listed. On other exchanges, the ""Depository Receipts"" are listed. i.e. the Company will keep say 100,000 shares with the primary stock exchange / depository. Based on this it would create new instruments ""Depository Receipts"". They can be 1:1 or whatever ratio. hypothetically, if I want to buy all of the company's stock Even if it is on one exchange, buying all stocks would trigger various regulatory aspects of Companies Act, or Stock Exchange rules. This is not simple or easy like clicking some buttons and buying everything. That is, let's say that in New York the company has listed 1000 shares, and in London only 10 shares, each worth 10 USD Market capitalization is sum of all outstanding shares into value." If you intend to be responsive to news and intraday price moves, for foreign stocks these will often happen while you're asleep (e.g. the Tokyo Stock Exchange opens at roughly midnight UK time). If I understand you correctly, you are noticing that a stock's price can change drastically when the time changes from pre-market trading hours to open market hours. This could occur because a much smaller pool of investors make trades during pre-market and after-market hours. When the regular market opens there is a large influx of trades, causing the prices to jump. Short answer: Liquidity. Well, you have to see it from an exchange's point of view.  Every contract they put up is a liability to them.  You have to allocate resources for the order book, the matching engine, the clearing, etc.  But only if the contract is actually trading they start earning (the big) money. Now for every new expiry they engage a long term commitment and it might take years for an option chain to be widely accepted (and hence before they're profitable).  Compare the volumes and open interests of big chains versus the weeklies and you'll find that weeklies can still be considered illiquid compared to their monthly cousins. Having said that, like many things, this is just a question of demand.  If there's a strong urge to trade July weeklies one day, there will be an option chain.  But, personally I think, as long as there are the summer doldrums there will be no rush to ask for Jul and Aug chains. If you check out China Stock Markets Web provides details on all things that trade on there. It covers the Hang Seng Index, SSE Index, and SSE Component Index. There is also tons of information for investors on the exchange website here.