Why I cannot buy at ask price?
The price is moving higher so by the time you enter your order and press buy, a new buyer has already come in at that time and taken out the lowest ask price. So you end up chasing the market as the prices keep moving higher. The solution: if you really want to be sure that you buy it and don't want to keep chasing the market higher and higher, you should put in a market order instead of a limit order. With a market order you may pay a few cents higher than the last traded price but you will be sure to have your order filled. If you keep placing limit orders you may miss out altogether, especially if the price keeps moving higher and higher. In a fast moving market a market order is always best if your aim is to be certain to buy the stock.
Some platforms/brokers have HTB indication for a stock symbol, meaning Hard To Borrow. That usually means you can't sell it short at the moment. 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. You are better off just placing a market order if you want to buy or sell straight away and avoid the queues. A market order will guarantee the purchase or sale of your shares, but it won't guarantee the price. "If the price used to be 2.50 but by the time you get in an order it's 2.80, you're going to have to pay 2.80. You can't say, ""I want to buy it at the price from an hour ago"". If you could, everybody would wait for the price to go up, then buy at the old price and have an instant guaranteed profit. Well, except that when you tried to sell, I suppose the buyer could say, ""I want to pay the lower price from last July"". So no, you always buy or sell at the current price. If you submit an order after the markets close, your broker should buy the stock for you as soon as possible the next morning. There's no strict queue. There are thousands of brokers out there, they don't take turns. So if your broker has 1000 orders and you are number 1000 on his list, while some other broker has 2 orders and number 1 is someone else wanting to buy the same stock, then even if you got your order in first, the other guy will probably get the first buy. LIFO and FIFO refer to any sort of list or queue, but don't really make sense here. When the market opens a broker has a list of orders he received overnight, which he might think of as a queue. He presumably works his way down the list. But whether he follows a strict and simple first-in-first-out, or does biggest orders first, or does buys for stocks he expects to go up today and sells for stocks he expects to go down today first, or what, I don't know. Does anybody on this forum know, are there rules that say brokers have to go through the overnight orders FIFO, or what is the common practice?" You can*, if the market is open, in a normal trading phase (no auction phase), works, and there is an existing bid or offer on the product you want to trade, at the time the market learns of your order. Keep in mind there are 2 prices: bid and offer. If the current bid and current offer were the same, it would immediately result in a trade, and thus the bid and offer are no longer the same. Market Makers are paid / given lower fees in order to maintain buy and sell prices (called quotes) at most times. These conditions are usually all true, but commonly fail for these reasons: Most markets have an order type of market order that says buy/sell at any price. There are still sanity checks put in place on the price, with the exact rules for valid prices depending on the stock, so unless it's a penny stock you won't suddenly pay ten times a stock's value. *The amount you can buy sell is limited by the quantity that exists on the bid and offer. If there is a bid or offer, the quantity is always at least 1. In order to see whether you can buy or sell some given quantity of a stock at the current bid price, you need a counterparty (a buyer) who is willing to buy the number of stocks you are wishing to offload. To see whether such a counterparty exists, you can look at the stock's order book, or level two feed. The order book shows all the people who have placed buy or sell orders, the price they are willing to pay, and the quantity they demand at that price. Here is the order book from earlier this morning for the British pharmaceutical company, GlaxoSmithKline PLC.  Let's start by looking at the left-hand blue part of the book, beneath the yellow strip. This is called the Buy side. The book is sorted with the highest price at the top, because this is the best price that a seller can presently obtain. If several buyers bid at the same price, then the oldest entry on the book takes precedence. You can see we have five buyers each willing to pay 1543.0 p (that's 1543 British pence, or £15.43) per share. Therefore the current bid price for this instrument is 1543.0. The first buyer wants 175 shares, the next, 300, and so on. The total volume that is demanded at 1543.0p is 2435 shares. This information is summarized on the yellow strip: 5 buyers, total volume of 2435, at 1543.0. These are all buyers who want to buy right now and the exchange will make the trade happen immediately if you put in a sell order for 1543.0 p or less. If you want to sell 2435 shares or fewer, you are good to go. The important thing to note is that once you sell these bidders a total of 2435 shares, then their orders are fulfilled and they will be removed from the order book. At this point, the next bidder is promoted up the book; but his price is 1542.5, 0.5 p lower than before. Absent any further changes to the order book, the bid price will decrease to 1542.5 p. This makes sense because you are selling a lot of shares so you'd expect the market price to be depressed. This information will be disseminated to the level one feed and the level one graph of the stock price will be updated. Thus if you have more than 2435 shares to sell, you cannot expect to execute your order at the bid price in one go. Of course, the more shares you are trying to get rid of, the further down the buy side you will have to go. In reality for a highly liquid stock as this, the order book receives many amendments per second and it is unlikely that your trade would make much difference. On the right hand side of the display you can see the recent trades: these are the times the trades were done (or notified to the exchange), the price of the trade, the volume and the trade type (AT means automatic trade).  GlaxoSmithKline is a highly liquid stock with many willing buyers and sellers. But some stocks are less liquid. In order to enable traders to find a counterparty at short notice, exchanges often require less liquid stocks to have market makers. A market maker places buy and sell orders simultaneously, with a spread between the two prices so that they can profit from each transaction. For instance Diurnal Group PLC has had no trades today and no quotes. It has a more complicated order book, enabling both ordinary buyers and sellers to list if they wish, but market makers are separated out at the top. Here you can see that three market makers are providing liquidity on this stock, Peel Hunt (PEEL), Numis (NUMS) and Winterflood (WINS). They have a very unpalatable spread of over 5% between their bid and offer prices. Further in each case the sum total that they are willing to trade is 3000 shares. If you have more than three thousand Dirunal Group shares to sell, you would have to wait for the market makers to come back with a new quote after you'd sold the first 3000. "During market hours, there are a lot of dealers offering to buy and sell all exchange traded stocks. Dealers don't actually care about the company's fundamentals and they set their prices purely based on order flow. If more people start to buy than sell, the dealer notices his inventory going down and starts upping the price (both his bid and ask). There are also traders who may not be ""dealers"", but are willing to sell if the price goes high enough or buy if the price goes low enough. This keeps the prices humming along smoothly. During normal trading hours, if you buy something and turn around and sell it two minutes later, you'll probably be losing a couple cents per share. Outside normal market hours, the dealers who continue to have a bid and ask listed know that they don't have access to good price information --  there isn't a liquid market of continuous buying and selling for the dealer to set prices he considers safe. So what does he do? He widens the spread. He doesn't know what the market will open tomorrow at and doesn't know if he'll be able to react quickly to news. So instead of bidding $34.48 and offering at $34.52, he'll move that out to $33 and $36. The dealer still makes money sometimes off this because maybe some trader realized that he has options expiring tomorrow, or a short position that he's going to get a margin call on, or some kind of event that pretty much forces him to trade. Or maybe he's just panicking and overreacting to some news. So why not trade after hours? Because there's no liquidity, and trading when there's no liquidity costs you a lot." I have done this, and the reason is to make sure that I don't run out of money in my account to place the order if there is an unexpected upswing in price. Suppose I have $1000 in my account and I want to buy 10 shares of ABCD that are currently at $99.  If the price doesn't change, then I am all set, but if the price goes up to $101 then I don't have sufficient funds to make the purchase. By placing a limit order at $100 I can ensure that I have enough money to place the order. In general, it is a rather unlikely scenario that it could happen, but placing the limit order is easy to do and it gives me peace of mind. I don't know what you mean about bypassing the queue. You can make a purchase at the after market price by sending an order that gets executed in after market. Often times these are called Extended orders, or EXT. With an EXT limit order it will place the bid on the after market hours order book. If you get filled, then you have the shares.  This is the answer. New to investing... when I buy/sell a stock can I buy/sell at the exact market price whenever I'd like or is there more to it? Does there need to be a demand for when I'm trying to sell or am I just forcing the company to buy back my shares? Sorry if confusing/rookie question Looking at the SPY option chain you posted, all of the call options with a strike price of 199.50 or higher have a bid of N/A.  That's because the ask price for all of those options is 0.01, and the bid price has to be less than the ask price, but buyers are not allowed to bid 0.00.  It's not accurate to say that no one wants to buy those calls - anyone who wanted to buy one of those calls would just buy it at the ask price of 0.01. So why are people selling those calls for just 0.01?  The further out of the money you go as you get closer to expiration, the less likely the underlying stock or ETF (SPY in this case) will go over the strike price, and the less you can sell it for.  SPY closed yesterday at about 195, and it would have to go up almost 2.5% today for the 199.50 calls to be in the money, and a 2.5% move in one day is extremely unlikely. Stop order is triggered when the market reaches the price you set. Until then - its not on the books. Your understanding is wrong in that you don't go to read the definition of the term. This question is impossible answer for all markets but there are 2 more possibilities in my experience: Oh really. I will have to check into that. It would be a bummer if that is the case. Something I will need to look into. If you don't need margin and are not trading the underlying asset (which I could see being a problem), then I don't see what the problem is. But I shall see. Thanks. Rule 610 (Google for it) stands that if Bid and Ask are the same, the market is considered Locked, and the exchange must stop all trading. So the same person can't quote the same bid and ask price. However, HFTs have found ways to circumvent this limitation when exchanges created special order types for them, e.g. Spam-and-Cancel