Which is the most liquid market for trading?
I would rate index futures, in particular the US index futures (e.g. the S&P 500 future) as the most liquid markets after the forex markets. Depends on how you measure liquidity.  There's papers out there that approach this very question. Measured in order book spreads for a consolidated $100m trade, I'd say the second biggest market is FX swaps, followed or par'd by the money market (government bonds). If you disallow OTC venues, it's most definitely exchange listed government bonds. If, however, you happen to think in terms of sheer volume per time, the most liquid market phase could be considered the NYSE closing auction, as you can move billions in a matter of minutes, or expressed in speed terms: several m$/s (million dollars per second). You should pick a definition and we can provide you with a more accurate list of candidates and actual data.
As Waldfee says, CFDs are a derivative (of the underlying stock in this case). If you are from the USA then they are prohibited in the USA as has also been mentioned. They are not prohibited, however, in many other countries including Australia.  We can buy or short sell (on a limited number of securities) CFDs on Australian securities, USA securities and securities from many other countries, on FX, and different commodities. The reason you are paying much less than the actial stock price is worth is because you are buying on margin. When you go long you pay interest on overnight positions, and when you go short you recieve interest on overnight positions (that is if you hold the position open overnight). Most CFDs are over the counter, however in Australia (don't know about other countries) we also have exchange traded CFDs called ASX CFDs. I have tried both ASX CFDs and over the counter CFDs and prefer the over the counter CFDs because the broker provides a market which closely but not exactly follows the underlying prices. Wlth the exchange traded CFDs there was low liquidity due to being quite new so there was the potential to be gapped quite considerably. This might improve as the market grows. All in all, once you understand how they work and what is involved in trading them, they are much easier than options or futers. However, if you are going to trade anything first get yourself educated, have a trading plan and risk management strategy, and paper trade before putting real money on the table. And remember, if you are in the USA, you are actually prohibited from trading CFDs. Regarding the price of AAPL at $50, the price should be the same as that of the underlying stock, it is just that your initial outlay will be less than buying the stock directly because you are buying on margin. Your initial outlay may be as little as 5% or lower, depending on the underlying stock. Differences in liquidity explain why American-style options are generally worth more than their European-style counterparts. As far as I can tell, no one mentioned liquidity in their answer to this question, they just introduced needlessly complex math and logic while ignoring basic economic principles. That's not to say the previous answers are all wrong - they just deal with periphery factors instead of the central cause.  Liquidity is a key determinant of pricing/valuation in financial markets. Liquidity simply describes the ease with which an asset can be bought and sold (converted to cash). Without going into the reasons why, treasury bills are one of the most liquid securities - they can be bought or sold almost instantly at any time for an exact price. The near-perfect liquidity of treasuries is one of the major reasons why the price (yield) of a t-bill will always be higher (lower yield) than that of an otherwise identical corporate or municipal bond. Stated in general terms, a relatively liquid asset is always worth more than an relatively illiquid asset, all else being equal.  The value of liquidity is easy to understand - we experience it everyday in real life. If you're buying a house or car, the ability to resell it if needed is an important component of the decision. It's the same for investors - most people would prefer an asset that they can quickly and easily liquidate if the need for cash arises.  It's no different with options. American-style options allow the holder to exercise (liquidate) at any time, whereas the buyer of a European option has his cash tied up until a specific date. Obviously, it rarely makes sense to exercise an option early in terms of net returns, but sometimes an investor has a desperate need for cash and this need outweighs the reduction in net profits from early exercise.  It could be argued that this liquidity advantage is eliminated by the fact that you can trade (sell) either type of option without restriction before expiration, thus closing the long position. This is a valid point, but it ignores the fact that there's always a buyer on the other side of an option trade, meaning the long position, and the right/restriction of early exercise, is never eliminated, it simply changes hands. It follows that the American-style liquidity advantage increases an options market value regardless of one's position (call/put or short/long). Without putting an exact number on it, the general interest rate (time value of money) could be used to approximate the additional cost of an American-style option over a similar European-style contract. Some liquidity Since you're using IB, and you seem to be an investor not a trader, so you won't notice especially if you walk your orders, but you will suffer the bid/ask spread as everyone else albeit wider.   If buying, the best strategy unless if one is time constrained is to walk the entire bid from the best bid to the best ask.  It is highly likely that someone will hit your order before you hit the best ask.  If they don't, as a long term investor, the few pennies won't make or break you, especially if the price per share is 100 USD equivalent, but it is an excellent habit to form and fun. Since you're buying ETFs, even though your orders are small, you would be adding liquidity to your market, helping it become more efficient because your orders could be used to arbitrage against all of the ETF's holdings, in turn providing liquidity for those holdings. No liquidity This could only be done with an extremely low cost broker like IB because the trading commissions would make it prohibitively expensive. There are huge risks when trading an illiquid security such as VEUR.  EWL would be much less risky thus less expensive. Securities with no liquidity can be traded, but they must be traded very carefully.  In the case of a security that can only attract about 20 shares per day in volume, only single shares should be bid.  The market makers, suffering from a dearth in volume may not even be willing to haggle; therefore, the only recourse is a statistical arbitrageur, who will attempt to profit from the spread between other more liquid versions of the security. Considering the available alternative, VEUR is not recommended to trade. "First it is worth noting the two sided nature of the contracts (long one currency/short a second) make leverage in currencies over a diverse set of clients generally less of a problem.  In equities, since most margin investors are long ""equities"" making it more likely that large margin calls will all be made at the same time. Also, it's worth noting that high-frequency traders often highly levered make up a large portion of all volume in all liquid markets ~70% in equity markets for instance.  Would you call that grossly artificial?  What is that volume number really telling us anyway in that case? The major players holding long-term positions in the FX markets are large banks (non-investment arm), central banks and corporations and unlike equity markets which can nearly slow to a trickle currency markets need to keep trading just for many of those corporations/banks to do business.  This kind of depth allows these brokers to even consider offering 400-to-1 leverage.  I'm not suggesting that it is a good idea for these brokers, but the liquidity in currency markets is much deeper than their costumers." I have been trading Forex and Futures as an independant Trader for almost 3 Years now, and unfortunately i have to agree with pizzlepaps statement that if you have to ask you probably should not be doing it at all.  There is a bunch of information out there on futures trading but then again im wondering which futures exactly you want to trade? Are we talking about ES contracts? Dax Contracts? Dow Contracts? Crude Contracts?  I mean im going to be honest here i really would like to be of help here but quite frankly i dont know how based on your question, so for now stay away from the futures market until you have done some heavy reading and defined your goals. 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. Trading at the start of the day is highest because of news flows that may have come after the close of the previous day.  And trading at the end of the day is highest because of expected news flows after closing hours. Moreover, there are many day traders who buy in the morning without making any payment for purchase and such traders have to sell by evening or else they will have to make the payment for the purchases which they have made. most def.  When I have an algorithmic trading strategy I want to spitball, or some question about how to exploit netback pricing inefficiency between West Texas Intermediate and Brent prices based on some sort of shipping rate change, I'd like to post here.  When I want a new job, I'll go to r/financialcareers.