Is there a significant danger to market orders as opposed to limit orders?
If you want your order to go through no matter what then you should be using market orders rather than limit orders. With limit orders you may get the price you are after or better but you are not guaranteed to get your order transacted. With a market order you are guaranteed to get you order transacted but may get a price inferior to what you were after. Most times this should only be a few cents but can get much larger in a fast moving or less liquid market. You should incorporate this slippage into your trading plan. Maybe a better option for you, if you are looking at + or - 0.5% from the last price, would be to use conditional triggers (stop buy and sell orders) with your market orders. Once the market moves in your direction your conditional order will be triggered and the stock will be bought at current market price. The Key aspect is the risk of market orders;   You should be worried about point 2 & 3 when you are doing market orders. "The risk of market orders depends heavily on the size of the market and the exchange. On big exchange and a security which is traded in hue numbers you're likely that there are enough participants to give you a ""fair"" price. Doing a market order on a security which is hardly dealed you might make a bad deal. In Germany Tradegate Exchange and the sister company the bank Tradegate AG are known to play a bit dirty: Their market is open longer than Frankfurt (Xetra) and has way lower liquidity. So it can happen that not all sell or buy orders can be processes on the Exchange and open orders are kept. Then Tradegate AG steps in with a new offer to full-fill these trades selling high or buying low. There is a German article going in details on wiwo.de either German or via Google Translate"
"First of all, not all brokers allow trading during pre-market and post-market.  Some brokers only allow trading during the regular hours (9:30am - 4pm ET). Second of all, while you can place orders using limit orders and market orders during regular trading hours, you can only use limit orders during pre-market and post-market.  This is because the liquidity is much lower during pre-market and post-market, and using market orders could result in some trades filling at horrible prices.  So brokers don't allow using market orders outside of regular trading hours. Third, some brokers require you to specify that you want your order to be executed during pre-market or post-market.  For example, my broker allows me to specify either ""Day"" or ""Ext"" for my orders.  ""Day"" means I want my order to execute only during regular trading hours, and ""Ext"" means I want my order to execute at any time - pre-market, regular trading hours, or post-market. Finally, if your broker allows pre/post market trading, and you place a limit order while specifying ""Ext"", then your trade can happen in real-time during pre-market or post-market.  Per your example, if a stock is trading at $5 at 8am, and you put in a limit order (while specifying ""Ext"") to buy it at $5 at 8am, then your order will execute at that time and you will buy that stock at 8am." In simple terms, this is how the shares are traded, however most of the times market orders are placed. Consider below scenario( hypothetical scenario, there are just 2 traders) Buyer is ready to buy 10 shares @ 5$ and seller is ready to sell 10 shares @ 5.10$, both the orders will remain in open state, unless one wish to change his price, this is an example of limit order. Market orders If seller is ready to sell 10 shares @ 5$ and another 10 shares @5.05$, if buyer wants to buy 20 shares @ market price, then the trade will be executed for 10 shares @ 5$ and another 10 shares @ 5.05$ I don't have all the answers. On a illiquid stock, such situations do arise and there are specific mechanisms used by exchanges to match the order. It is generally not advisable to use market order on illiquid stock. There are lots of different variations here. I guess this comes down to specifications for individual exchanges, but I'm wondering if there's a standard here or a way to approach it from basic rules that clears up all these situations. There are quite a few variations and different treatments. Market order that are placed when the market is closed or just around market opening are traded at Market Open price that each exchange has a formulae to calculate. In the process Market Buy are matched to Market Sell at the Exchange calculated price. Not all order get matched and there could be spill over's. These are then matched to limit orders. Is this determined based on which sell order came first, or based on which would result in the best deal for the incoming buyer? Generally Market orders have highest priority of execution. Because in the case for 100/101, if you wanted to placed a limit buy order at top of the bid list you would place it at 101 and get filled straight away. If placing a limit buy order at the top of 91 (for 90/98) you would not get filled but just be placed at the top of the list. You might get filled at a lower price if an ask comes in matching your bid, however you might never get filled. In regards to market orders, with the 100/101 being more liquid, if your market order is larger than the orders at 101, then the remainder of your order should still get filled at only a slightly higher price. In regards to market orders with the 90/98, being less liquid, it is likely that only part of your order gets filled, and any remained either doesn't get filled or gets filled at a much higher price. If you are in it for the long run and are not worried about intra day fluctuations and buying within + or - 1% you would be better off going for a market order as this will make sure you buy it on the day.  If you use limit orders you risk missing out on the order if prices gap and start rising in the morning. Another option is to employ stop buy trigger orders (if offered by your broker). So you would have to sum up and decide which type of order would suit your strategy the best. Are you looking to buy the security because you are looking for long term growth and gains, or are you after getting the best price possible to help your short term gains? At any point of time, buyer wants to purchase a stock at lesser price and seller wants to sell the stock at a higher price.  Let's consider this scenario  Company XYZ is trading at 100$, as stated above buyer wants to purchase at lower price and seller at higher price, this information will be available in Market depth, let's consider there are 5 buyers and 5 sellers, below are the details of their orders Buyers List Sellers List Highest order in buyers list will contain the bid price and bid quantity, Lowest order in Sellers list will contain the offer price and offer quantity. Now, if I want to buy 50 Stocks of company XYZ, need to place an order first, it can be either limit or Market. Limit Order : In this order, I will mention the price(buy price) at which I wish to buy, if there is any seller selling the stock less than or equal to price I have mentioned, then the order will be executed else it will be added to buyers list Market Order : In this order, I will not mention the price, if I wish to purchase 50 Stocks, then it will find the lowest offer price and buy stocks, in our case it will be 101. if I wish to purchase 200 Stocks, then it will find the lowest offer price and buy stocks, in our case it will be 2 transactions, since entire request cannot be accommodated in single order Usually the volume(Ask Volume and Offer Volume) being displayed are all Limit orders and not Market orders, Market orders are executed immediately. This is just an example, However several transactions are executed within a second, hence we will get to know the exact value only after the order is completed(executed) If a market is efficient then risk/reward should be linear.  In simple markets like stocks and bonds, everyone thinks the same way and the risk/reward calculation is simple, so everyone can have an accurate idea of the risk/reward ratio, unless the company has serious undisclosed problems. But in other markets like derivatives and mortgage bonds, few people understand what they're buying so the risks remain hidden. Someone might think a company will do well, so they buy an derivative on that company. But no one understands risk/reward calculations on derivatives, so the risk/reward on the derivative could be way off the price on the derivative. "You can interpret prices in any way you wish, but the commonly quoted ""price"" is the last price traded. If your broker routes those orders, unlikely because they will be considered ""unfair"" and will probably be busted by the exchange, the only way to drive the price to the heights & lows in your example is to have an overwhelming amount of quantity relative to the order book. Your orders will hit the opposing limit orders until your quantity is exhausted, starting from the best price to the worst price. This is the functional equivalent to a market order."