Do market shares exhaust?
"As @ApplePie pointed out in their answer, at any given time there is a finite amount of stock available in a company. One subtlety you may be missing is that there is always a price associated with an offer to buy shares. That is, you don't put in an order simply to buy 1 share of ABC, you put in an order to buy 1 share of ABC for $10. If no one is willing to sell a share of ABC for $10, then your order will go unfilled. This happens millions of times a day as traders try to figure the cheapest price they can get for a stock. Practically speaking, there is always a price at which people are willing to sell their shares. You can put in a market order for 1 share of ABC, which says essentially ""I want one share of ABC, and I will pay whatever the market deems to be the price"". Your broker will find you 1 share, but you may be very unhappy about the price you have to pay! While it's very rare for a market to have nobody willing to sell at any price, it occasionally happens that no one is willing to buy at any price. This causes a market crash, as in the 2007-2008 financial crisis, when suddenly everyone became very suspicious of how much debt the major banks actually held, and for a few days, very few traders were willing to buy bank stocks at any price." Let's clarify some things. Companies allow for the public to purchase their shares through Initial Public Offering (IPO) (first-time) and Seasoned Public Offering (SPO) (all other times). They choose however many shares they want to issue depending on the amount of capital they want to raise. What this means is that the current owners give up some ownership % in exchange for cash (usually). In the course of IPOs and SPOs, it can happen that the public will not buy all shares if there is very little interest, but I would assume that the more probable scenario if very little interest is present is that the shares' value would take a big drop on their issuance date from the proposed IPO/SPO price. After those shares are bought by the public, they are traded on Exchanges which are a secondary and (mostly) do not affect the underlying company. The shares are exchanged from John Doe to Jane Doe as John Doe believes the market value for those shares will take a direction that Jane Doe believes in the opposite. Generally speaking, markets will find an equilibrium price where you can reasonably easily buy-sell securities as the price is not too far from what most participants in the market believe it should be. In cases where all participants agree on the direction (most often in case of a crash) it can be hard to find a party to make a trade with. Say a company just announced negative news with long-lasting effects on the business there will be a surge in sell orders with very few buyers. If you are willing to buy, you will likely very easily find a trading partner but if you are trying to sell instead then you will have to compete for the lowest price against all other sellers. All that to say that in such cases, while shares are technically sellable / purchasable, the end result can be that no shares are purchasable. RonJohn is right, all shares are owned by someone.  Depending on the company, they can be closely held so that nobody wants to sell at a given time.  This can cause the price people are offering to rise until someone sells.  That trade will cause an adjustment in the ticker price of that stock.  Supply and demand at work.  Berkshire Hathaway is an example of this.  The number of shares is low, the demand for them is high, the price per share is high. Yes, all the shares of a publicly traded company can be purchased. This effectively takes the company private so that it's no longer traded on a stock market. Here are some examples: EDIT: to answer your edited question... the corporation can issue more stock.  However that would dilute the value of existing shares.  Thus, existing shareholders must vote to allow more shares to be issued. So... in your situation yes, you'd need to wait for someone else to sell. Stock trades are always between real buyers and real sellers. In thinly-traded small stocks, for example, you may not always be able to find a buyer when you want to sell. For most public companies, there is enough volume that individual investors can just about always fill their market orders. If the share is listed on a stock exchange that creates liquidity and orderly sales with specialist market makers, such as the NYSE, there will always be a counterparty to trade with, though they will let the price rise or fall to meet other open interest.  On other exchanges, or in closely held or private equity scenarios, this is not necessarily the case (NASDAQ has market maker firms that maintain the bid-ask spread and can do the same thing with their own inventory as the specialists, but are not required to by the brokerage rules as the NYSE brokers are).  The NYSE has listing requirements of at least 1.1 million shares, so there will not be a case with only 100 shares on this exchange. Everyone has a price. If nobody is selling shares, then increase the price you will buy them for. And then wait. Somebody will have some hospital bills to pay for eventually. I buy illiquid investments all the time, and thats typically what happens. Great companies do not have liquidity problems.
Buffet is able to do many things the average investor cannot do.  For example: During the 2008 market crash Buffet purchased 5 Billion on Citi preferred stock (as somewhat of a bail out) that pays 5% Dividend. Then he also received warrants to buy another 700 million shares over the next 10 years where he can buy shares at 5% discount. So right off the bat he is up 5% anytime he buys some of those 700 million shares. http://dealbook.nytimes.com/2011/08/25/buffett-to-invest-5-billion-in-bank-of-america/?_php=true&_type=blogs&_r=0 This is just one of the Buffet deal makings. With his cash you can move markets.  He buys, people hear about it, they buy, his positions go up.  Put that aside he loans cash, gets interest, buys companies. It is more than just investing in the stock market. When you buy shares, you are literally buying a share of the company.  You become a part-owner of it. Companies are not required to pay dividends in any given year.  It's up to them to decide each year how much to pay out. The value of the shares goes up and down depending on how much the markets consider the company is worth.  If the company is successful, the price of the shares goes up.  If it's unsuccessful, the price goes down.  You have no control over that.  If the company fails completely and goes bankrupt, then the shares are worthless. Dilution is where the company decides to sell more shares.  If they are being sold at market value, then you haven't really lost anything.  But if they are sold below cost (perhaps as an incentive to certain staff), then the value of the company per share is now less.  So your shares may be worth a bit less than they were.  You would get to vote at the AGM on such schemes.  But unless you own a significant proportion of the shares in the company, your vote will probably make no difference. In practice, you can't protect yourself.  Buying shares is a gamble.  All you can do is decide what to gamble on. "I have heard that investing more money into an investment which has   gone down is generally a bad idea*. ""Throwing good money after bad"" so   to speak. Is investing more money into a stock, you already have a stake in,   which has gone up in price; a good idea? Other things being equal, deciding whether to buy more stocks or shares in a company you're already invested in should be made in the same way you would evaluate any investment decision and -- broadly speaking -- should not be influenced by whether an existing holding has gone up or down in value. For instance, given the current price of the stock, prevailing market conditions, and knowledge about the company, if you think there is a reasonable chance that the price will rise in the time-period you are interested in, then you may want to buy (more) stock. If you think there is a reasonable chance the price will fall, then you probably won't want to buy (more) stock. Note: it may be that the past performance of a company is factored into your decision to buy (e.g was a recent downturn merely a ""blip"", and long-term prospects remain good; or have recent steady rises exhausted the potential for growth for the time being). And while this past performance will have played a part in whether any existing holding went up or down in value, it should only be the past performance -- not whether or not you've gained or lost money -- that affects the new decision. For instance: let us suppose (for reasons that seemed valid at the time) you bought your original holding at £10/share, the price has dropped to £2/share, but you (now) believe both prices were/are ""wrong"" and that the ""true price"" should be around £5/share. If you feel there is a good chance of this being achieved then buying shares at £2, anticipating they'll rally to £5, may be sound. But you should be doing this because you think the price will rise to £5, and not because it will offset the loses in your original holding. (You may also want to take stock and evaluate why you thought it a good idea to buy at £10... if you were overly optimistic then, you should probably be asking yourself whether your current decisions (in this or any share) are ""sound""). There is one area where an existing holding does come into play: as both jamesqf and Victor rightly point out, keeping a ""balanced"" portfolio -- without putting ""all your eggs in one basket"" -- is generally sound advice. So when considering the purchase of additional stock in a company you are already invested in, remember to look at the combined total (old and new) when evaluating how the (potential) purchase will affect your overall portfolio." "There are two distinct questions that may be of interest to you. Both questions are relevant for funds that need to buy or sell large orders that you are talking about. The answer depends on your order type and the current market state such as the level 2 order book. Suppose there are no iceberg or hidden orders and the order book (image courtesy of this question) currently is:  An unlimited (""at market"") buy order for 12,000 shares gets filled immediately: it gets 1,100 shares at 180.03 (1,100@180.03), 9,700 at 180.04 and 1,200 at 180.05. After this order, the lowest ask price becomes 180.05 and the highest bid is obviously still 180.02 (because the previous order was a 'market order'). A limited buy order for 12,000 shares with a price limit of 180.04 gets the first two fills just like the market order: 1,100 shares at 180.03 and 9,700 at 180.04. However, the remainder of the order will establish a new bid price level for 1,200 shares at 180.04. It is possible to enter an unlimited buy order that exhausts the book. However, such a trade would often be considered a mis-trade and either (i) be cancelled by the broker, (ii) be cancelled or undone by the exchange, or (iii) hit the maximum price move a stock is allowed per day (""limit up""). Funds and banks often have to buy or sell large quantities, just like you have described. However they usually do not punch through order book levels as I described before. Instead they would spread out the order over time and buy a smaller quantity several times throughout the day. Simple algorithms attempt to get a price close to the time-weighted average price (TWAP) or volume-weighted average price (VWAP) and would buy a smaller amount every N minutes. Despite splitting the order into smaller pieces the price usually moves against the trader for many reasons. There are many models to estimate the market impact of an order before executing it and many brokers have their own model, for example Deutsche Bank. There is considerable research on ""market impact"" if you are interested. I understand the general principal that when significant buy orders   comes in relative to the sell orders price goes up and when a   significant sell order comes in relative to buy orders it goes down. I consider this statement wrong or at least misleading. First, stocks can jump in price without or with very little volume. Consider a company that releases a negative earnings surprise over night. On the next day the stock may open 20% lower without any orders having matched for any price in between. The price moved because the perception of the stocks value changed, not because of buy or sell pressure. Second, buy and sell pressure have an effect on the price because of the underlying reason, and not necessarily/only because of the mechanics of the market. Assume you were prepared to sell HyperNanoTech stock, but suddenly there's a lot of buzz and your colleagues are talking about buying it. Would you still sell it for the same price? I wouldn't. I would try to find out how much they are prepared to buy it for. In other words, buy pressure can be the consequence of successful marketing of the stock and the marketing buzz is what changes the price." Markets are rational in the long term. Actors act rationally given the knowledge they have. They don't have perfect knowledge - meaning they're prone to make mistakes. However, in the LONG run, every would be a equilibrium.   Facebook stock is clearly over valued and the market is adjusting to the real price. Nothing spectacular going on there. "Past results are not a predictor of future results. There is no explicit upper bound on a market, and even if individual companies' values were remaining unchanged one would expect the market to drift upward in the long term. Plus, there's been some  shift from managing companies for dividends to managing stocks for growth, which will tend to increase the upward push. Trying to time the market -- to guess when it's going to move in any particular direction -- is usually closer to gambling than investing. The simplest answer remains a combination of buy-and-hold and dollar-cost averaging. Buy at a constant number of dollars per month (or whatever frequency you prefer), and you will automatically buy more when the stock/fund is lower, less when it is higher. That takes advantage of downturns as buying opportunities without missing out on possible gains at the other end. Personally, I add a bit of contrarian buying to that -- I increased my buying another notch or two while the market was depressed, since I had money I wouldn't need any time soon (buy and hold) and I was reasonably confident that enough of the market would come back strongly enough that I wasn't at significant risk of losing the investment. That's one of the things which causes me to be categorized as an ""aggressive investor"" even though I'm operating with a very vanilla mix of mutual funds and not attempting to micromanage my money. My goal is to have the money work for me, not vice versa." "Yahoo's ""Adj Close"" data is adjusted for splits, but not for dividends. Despite Yahoo's webpage's footnote saying  *Close price adjusted for dividends and splits. we can see empirically that the ""Adj Close"" is only adjusted for splits. For example, consider Siemens from Jan 27, 2017 to Mar 15, 2017: The Adj Close adjusts for splits: On any particular day, the ""Adj Close"" is equal to the ""Close"" price divided by the cumulative product of all splits that occurred after that day. If there have been no splits after that day, then the ""Adj Close"" equals the ""Close"" price. Since there is a 2-for-1 split on Mar 14, 2017, the Adj Close is half the Close price for all dates from Jan 27, 2017 to Mar 13, 2017. Note that if Siemens were to split again at some time in the future, the Adj Close prices will be readjusted for this future split. For example, if Siemens were to split 3-for-1 tomorrow, then all the Adj Close prices seen above will be divided by 3. The Adj Close is thus showing the price that a share would have traded on that day if the shares had already been split in accordance with all splits up to today. The Adj Close does not adjust for dividends: Notice that Siemens distributed a $1.87 dividend on Feb 02, 2017 and ~$3.74 dividend on Jan 30, 2017. If the Adj Close value were adjusted for these dividends then we should expect the Adj Close should no longer be exactly half of the Close amount. But we can see that there is no such adjustment -- the Adj Close remains (up to rounding) exactly half the Close amount: Note that in theory, the market reacts to the distribution of dividends by reducing the trading price of shares post-dividend. This in turn is reflected in the raw closing price. So in that sense the Adj Close is also automatically adjusted for dividends. But there is no formula for this. The effect is already baked in through the market's closing prices." Usually when a stock is up-trending or down-trending the price does not go up or down in a straight line. In an uptrend the price may go up over a couple of days then it could go down the next day or two, but the general direction would be up over the medium term. The opposite for a downtrend. So if the stock has been generally going up over the last few weeks, it may take a breather for a week or two before prices continue up again. This breather is called a retracement in the uptrend. The Fibonacci levels are possible amounts by which the price might retract before it continues on its way up again. By the way 50% is not actually a Fibonacci Retracement level but it is a common retracement level which is usually used in combination with the Fibonacci Retracement levels.