When shorting a stock, do you pay current market price or the best (lowest) available ask price?
When you want to short a stock, you are trying to sell shares (that you are borrowing from your broker), therefore you need buyers for the shares you are selling.  The ask prices represent people who are trying to sell shares, and the bid prices represent people who are trying to buy shares. Using your example, you could put in a limit order to short (sell) 1000 shares at $3.01, meaning that your order would become the ask price at $3.01.  There is an ask price ahead of you for 500 shares at $3.00.  So people would have to buy those 500 shares at $3.00 before anyone could buy your 1000 shares at $3.01. But it's possible that your order to sell 1000 shares at $3.01 never gets filled, if the buyers don't buy all the shares ahead of you.  The price could drop to $1.00 without hitting $3.01 and you will have missed out on the trade. If you really wanted to short 1000 shares, you could use a market order.  Let's say there's a bid for 750 shares at $2.50, and another bid for 250 shares at $2.49.  If you entered a market order to sell 1000 shares, your order would get filled at the best bid prices, so first you would sell 750 shares at $2.50 and then you would sell 250 shares at $2.49. I was just using your example to explain things.  In reality there won't be such a wide spread between the bid and ask prices.  A stock might have a bid price of $10.50 and an ask price of $10.51, so there would only be a 1 cent difference between putting in a limit order to sell 1000 shares at $10.51 and just using a market order to sell 1000 shares and getting them filled at $10.50. Also, your example probably wouldn't work in real life, because brokers typically don't allow people to short stocks that are trading under $5 per share. As for your question about how often you are unable to make a short sale, it can sometimes happen with stocks that are heavily shorted and your broker may not be able to find any more shares to borrow. Also remember that you can only short stocks with a margin account, you cannot short stocks with a cash account. In terms of pricing the asset, this functions in exactly the same way as a regular sell, so bids will have to be hit to fill the trade. When shorting an equity, currency is not borrowed; the equity is, so the value of per share liability is equal to it's last traded price or the ask if the equity is illiquid. Thus when opening a short position, the asks offer nothing to the process except competition for your order getting filled. Part of managing the trade is the interest rate risk.  If the asks are as illiquid as detailed in the question, it may be difficult even to locate the shares for borrowing. As a general rule, only illiquid  equities or those in free fall may be temporarily unable for shorting. Interactive Brokers posts their securities financing availabilities and could be used as a proxy guide for your broker. I would never use a market order.  Some brokerages have an approval process your short-sale goes through before going to market.  This can take some time.  So the market prices may well be quite different later. Some brokerages use a separate account for short sales, so you must get their approval for the account before you can do the trade.   I like the listing of shares available for shorting the Interactive Brokers has but I have experienced orders simply going into dead-air and sitting there on the screen, not being rejected, not going to market, not doing anything --- even though the shares are on the list.
Adding to the answers above, there is another source of risk: if one of the companies you are short receives a bid to be purchased by another company, the price will most probably rocket... "And what exactly do I profit from the short? I understand it is the difference in the value of the stock. So if my initial investment was $4000 (200 * $20) and I bought it at $3800 (200 * $19) I profit from the difference, which is $200. Do I also receive back the extra $2000 I gave the bank to perform the trade? Either this is extremely poorly worded or you misunderstand the mechanics of a short position.  When you open a short position, your are expecting that the stock will decline from here.  In a short position you are borrowing shares you don't own and selling them.  If the price goes down you get to buy the same shares back for less money and return them to the person you borrowed from.  Your profit is the delta between the original sell price and the new lower buy price (less commissions and fees/interest).  Opening and closing a short position is two trades, a sell then a buy.  Just like a long trade there is no maximum holding period. If you place your order to sell (short) 200 shares at $19, your initial investment is $3,800.   In order to open your $3,800 short position your broker may require your account to have at least $5,700 (according to the 1.5 ratio in your question).  It's not advisable to open a short position this close to the ratio requirement.  Most brokers require a buffer in your account in case the stock goes up, because in a short trade if the stock goes up you're losing money.  If the stock goes up such that you've exhausted your buffer you'll receive what's known as a ""margin call"" where your broker either requires you to wire in more money or sell part or all of your position at a loss to avoid further losses.  And remember, you may be charged interest on the value of the shares you're borrowing. When you hold a position long your maximum loss is the money you put in; a position can only fall to zero (though you may owe interest or other fees if you're trading on margin).  When you hold a position short your maximum loss is unlimited; there's no limit to how high the value of something can go.  There are less risky ways to make short trades by using put options, but you should ensure that you have a firm grasp on what's happening before you use real money. The timing of the trades and execution of the trades is no different than when you take a plain vanilla long position.  You place your order, either market or limit or whatever, and it executes when your trade criteria occurs." I stock is only worth what someone will pay for it.  If you want to sell it you will get market price which is the bid. This is a gross simplification as there are a few different ways to do this. The principle overall is the same though. To short a stock, you borrow X shares from a third party and sell them at the current price. You now owe the lender X shares but have the proceeds from the sale. If the share price falls you can buy back those shares at the new lower price, return them to the lender and pocket the difference. The risk comes when the share price goes the other way, you now owe the lender the new value of the shares, so have to find some way to cover the difference. This happened a while back when Porsche made a fortune buying shares in Volkswagen from short sellers, and the price unexpectedly rose. "When you place a limit sell order of $10.00 (for a stock on an option) you are adding your order to the book.  Anyone who places a buy at-the-market or with a limit price over $10.00 will have that order immediately fulfilled through the offer you have placed on the book. On the other hand, if that other person places a buy for $8.00, then the spread will now be ""$8.00 bid, $10.00 ask"". Priority is based on first the price (all $9.99 asks will clear before $10.00) and within each bucket this is based on the time your order was submitted. This is why in bidding markets (including eBay) buying at $x.01 is way better than $x.00 and selling at $x.99 is better than $(x+1).00. Source: https://en.wikipedia.org/wiki/Order_(exchange) under ""first-come-first-served""" "First, you are not exactly ""giving"" the brokerage $2000. That money is the margin requirement to protect them in the case the stock price rises. If you short 200 shares as in your example and they are holding $6000 from you then they are protected in the event of the stock price increasing to $30/share. Sometime before it gets there the brokerage will require you to deposit more money or they will cover your position by repurchasing the shares for your account. The way you make money on the short sale is if the stock price declines. It is a buy low sell high idea but in reverse. If you believe that prices are going to drop then you could sell now when it is high and buy back later when it is lower. In your example, you are selling 200 shares at $20 and later, buying those at $19. Thus, your profit is $200, not counting any interest or fees you have paid. It's a bit confusing because you are selling something you'll buy in the future. Selling short is usually considered quite risky as your gain is limited to the amount that you sold at initially (if I sell at $20/share the most I can make is if the stock declines to $0).  Your potential to lose is unlimited in theory. There is no limit to how high the stock could go in theory so I could end up buying it back at an infinitely high price. Neither of these extremes are likely but they do show the limits of your potential gain and loss.  I used $20/share for simplicity assuming you are shorting with a market order vs a limit order. If you are shorting it would be better for you to sell at 20 instead of 19 anyway. If someone says I would like to give you $20 for that item you are selling you aren't likely to tell them ""no, I'd really only like $19 for it""" "You are likely making an assumption that the ""Short call"" part of the article you refer to isn't making: that you own the underlying stock in the first place. Rather, selling short a call has two primary cases with considerably different risk profiles. When you short-sell (or ""write"") a call option on a stock, your position can either be: covered, which means you already own the underlying stock and will simply need to deliver it if you are assigned, or else uncovered (or naked), which means you do not own the underlying stock. Writing a covered call can be a relatively conservative trade, while writing a naked call (if your broker were to permit such) can be extremely risky. Consider: With an uncovered position, should you be assigned you will be required to buy the underlying at the prevailing price. This is a very real cost — certainly not an opportunity cost. Look a little further in the article you linked, to the Option strategies section, and you will see the covered call mentioned there. That's the kind of trade you describe in your example." I think George's answer explains fairly well why the brokerages don't allow this - it's not an exchange rule, it's just that the brokerage has to have the shares to lend, and normally those shares come from people's margin, which is impossible on a non-marginable stock. To address the question of what the alternatives are, on popular stocks like SIRI, a deep In-The-Money put is a fairly accurate emulation of an actual short interest.  If you look at the options on SIRI you will see that a $3 (or higher) put has a delta of -$1, which is the same delta as an actual short share. You also don't have to worry about problems like margin calls when buying options.  The only thing you have to worry about is the expiration date, which isn't generally a major issue if you're buying in-the-money options... unless you're very wrong about the direction of the stock, in which case you could lose everything, but that's always a risk with penny stocks no matter how you trade them. At least with a put option, the maximum amount you can lose is whatever you spent on the contract.  With a short sale, a bull rush on the stock could potentially wipe out your entire margin.  That's why, when betting on downward motion in a microcap or penny stock, I actually prefer to use options.  Just be aware that option contracts can generally only move in increments of $0.05, and that your brokerage will probably impose a bid-ask spread of up to $0.10, so the share price has to move down at least 10 cents (or 10% on a roughly $1 stock like SIRI) for you to just break even; definitely don't attempt to use this as a day-trading tool and go for longer expirations if you can. "Why would people sell below the current price, and not within the range of the bid/ask? There are many scenarios where this is deliberate but all of them boil down to the fact that the top level's bid doesn't support the quantity you're trying to sell (or is otherwise bogus[1]). One scenario as an example: You're day-trading both sides but at the end of the day you accumulated a rather substantial long position in a stock.  You don't want to (or aren't allowed to[2]) be exposed overnight, however.  What do you do? You place an order that is highly likely to go through altogether.  There's several ways to achieve that but a very simple one is to look at the minimum bid level for which the bid side is willing to take all of your shares, then place a limit order for the total quantity at that price.  If your position doesn't fit into the top level bid that price will well be lower than the ""current"" bid. Footnotes: [1] Keyword: quote stuffing [2] Keyword: overnight margin (aka positional margin, as opposed to intraday margin), this is highly broker dependent, exchanges don't usually distinguish between intraday and overnight margins, instead they use the collective term maintenance margin" The whole point of buying puts is cheaper cost and lower downside risk. If you short the box, you are assuming he already holds gold holdings to short against. It's not the same as short selling where you borrow shares.  Either way, you are far more vulnerable to downside risk if you are short the stock (whether you borrowed or shorted already owned shares). If Gold suddenly has a 20% pop over the next year, which could be possible given the volatility and uncertainty in the marketplace, you have big trouble. Whereas, if you buy puts, you only lose your costs for the contracts. The amount that you miss by in your bet isn't going to factor into anything. "A market sell order will be filled at the highest current ""bid"" price. For a reasonably liquid stock, there will be several buy orders in line, and the highest bid must be filled first, so there should a very short time between when you place the order and when it is filled.   What could happen is what's called front running. That's when the broker places their own order in front of yours to fulfill the current bid, selling their own stock at the slightly higher price, causing your sale to be filled at a lower price.  This is not only unethical but illegal as well. It is not something you should be concerned about with a large broker.   You should only place a market order when you don't care about minute differences between the current ask and your execution price, but want to guarantee order execution. If you absolutely have to sell at a minimum price, then a limit order is more appropriate, but you run the risk that your limit will not be reached and your order will not be filled. So the risk is a tradeoff between a guaranteed price and a guaranteed execution." "As others have noted, your definition of ""market price"" is a bit loose.  Really whatever price you get becomes the current market price.  What you usually get quoted are the current best bid and ask with the last transaction price.  For stocks that don't trade much, the last transaction price may not be representative of the current market value. Your question included regulation (""standards bureau""), and I don't think the current answers are addressing that.  In the US, the Securities and Exchange Commission (SEC) provides some regulation regarding execution price.  It goes by the designation Regulation NMS, and, very roughly, it says that each transaction has to take the best available price at the time that it is executed.  There are some subtleties, but that's the gist of it. No regulation ensures that there will be a counterparty to any transaction that you want to make.  It could happen, for example, that you have shares of some company that you're never able to sell because no one wants them. (BitCoin is the same in this regard.  There is a currently a market for BitCoin, but there's no regulation that ensures there will be a market for it tomorrow.) Outside of the US, I don't know what regulation, if any, exists." If you are buying your order will be placed in Bid list. If you are selling your order will be placed in the Ask list. The highest Bid price will be placed at the top of the Bid list and the lowest Ask price will be placed at the top of the Ask list. When a Bid and Ask price are matched a transaction will take place and it will the last traded price. If you are looking to buy at a lower price, say $155.01, your Bid price will be placed 3rd in the Bid list, and unless the Ask prices fall to that level, your order will remain in the list until it trades, it expires or you cancel it. If prices don't fall to you Bid price you will not get a trade. If you wanted your trade to go through you could either place a limit buy order closer to the lowest Ask price (however this is still not a certainty), or to be certain place a market buy order which will trade at the lowest Ask price. The 'normal' series of events when trading a stock is to buy it, time passes, then you sell it. If you believe the stock will drop in price, you can reverse the order, selling shares, waiting for the price drop, then buying them back. During that time you own say, -100 shares, and are 'short' those shares. Yes in order for you to short a stock, some one has to be willing to lend it to you to short, the more people that want to short this stock, the higher the borrowing rate is to short it. in some instances such as groupon so many people are shorting it that there are practically no shares left to short and if you do end up getting some it would be at a very high borrowing cost.