Can heavy demand for options drive up or down a stock price?
You will tend to find as options get closer to expiry (within 2 months of expiry) they tend to be traded more. Also the closer they are to being in the money they more they are traded. So there tends to be more demand for these options than long dated ones that are far out of the money. When there is this higher demand there is less need for a market maker to step in to assure liquidity, thus there should be no effect on the underlying stock price due to the high demand for options. I would say that market makers would mainly get involved in providing liquidity for options way out of the money and with long periods until expiry (6+ months), where there is little demand to start with and open interest is usually quite low.
Consider the mechanic which actually drives the 'price' of a stock. In simplest terms, the 'price' of a stock is the price at which the most recent trade occurred. ie: if the price of IBM is $100/share, that means the last time someone bought IBM stock, they paid $100. Above and below the 'spot price', are dozens/hundreds/thousands of buyers and sellers who have placed orders that no one is yet willing to match. ie: if IBM's spot price is at $100, there could still be 10,000 people willing to sell for $101 (called the 'ask' price, for the lowest price someone is currently willing to sell at), and 15,000 willing to buy for $99 (called the 'bid' price, for the highest price someone is currently willing to buy for).  Until someone is willing to buy for $101, then no one will be able to sell at $101. Until someone is willing to sell for $99, no one will be able to buy for $99. Typically orders are placed in the market at a particular limit. Meaning that those orders to buy at $99/sell at $101 are already in the 'system', and will be matched immediately as soon as someone is willing to meet the price on the other side. Now consider general market economics: high demand drives up price, and high supply drives down price. If the details above for IBM were yesterday, and today some news came out that IBM was laying off employees, imagine that another 10,000 people who held shares wanted to sell. Now there would be 20,000 sellers and only 15,000 buyers. If those new sellers were aggressive about wanting to sell, they would have to drop their price to $99, to match the highest buyers in the market. Put together, this means that as more sellers enter the market, supply of shares increases, driving down price. Conversely, as more buyers enter the market, demand for shares increases, driving up share price. As a result of the above, you can say that (all else being equal) if price for a stock goes up, there were more buyers that day, and if price goes down, there were more sellers that day. On the face of it, that is not necessarily true, because you could have the same number of buyers and sellers, one side could have simply decreased/increased their acceptable price to match the other side. Large volume just means a lot of market participants believe they know where the stock price will be (after some amount of time).  The fact that the price is not moving just means that about 50% of those really confident traders think the stock will be moving up, and about 50% of those really confident traders think the stock will be moving down. "Yes, long calls, and that's a good point. Let's see... if I bought one contract at the Bid price above...          $97.13 at expiry of $96.43 option = out of the money =- option price(x100)          = $113 loss.     $97.13 at expiry of $97.00 option = out of the money =- option price(x100)          = $77 loss.     $97.13 at expiry of $97.14 option = in the money by 1-cent=$1/contract profit - option price(x100) = $1-$58          = $57 loss   The higher strike prices have much lower losses if they expire with the  underlying stock at- or near-the-money. So, they carry ""gentler"" downside potential, and are priced much higher to reflect that ""controlled"" risk potential.  That makes sense. Thanks." Yes, that's the risk. If the stock is bouncing around a lot your options could get assigned.  If it heads south you now are the proud owner of more of a falling stock.  It's good that you're looking to understand the risks of an investment method.  That's important no matter what the method is. Typically a private company is hit by demand supply issues and cost of inputs. In effect at times the cost of input may go up, it cannot raise the prices, because this will reduce demand. However certain public sectors companies, typically in Oil & Engery segements the services are offered by Public sector companies, and the price they charge is governed by Regulatory authorities. In essence the PG&E, the agreement for price to customers would be calculated as cost of inputs to PG&E, Plus Expenses Plus 11.35% Profit. Thus the regulated price itself governs that the company makes atleast 11.35% profit year on year. Does this mean that the shares are good buy?  Just to give an example, say the price was $100 at face value, So essentially by year end logically you would have made 111.35/-. Assuming the company did not pay dividend ... Now lets say you began trading this share, there would be quite a few people who would say I am ready to pay $200 and even if I get 11.35 [on 200] it still means I have got ~6% return. Someone may be ready to pay $400, it still gives ~3% ... So in short the price of the stock would keep changing depending how the market percieves the value that a company would return. If the markets are down or the sentiments are down on energy sectors, the prices would go down.  So investing in PG&E is not a sure shot way of making money. For actual returns over the years see the graph at http://www.pgecorp.com/investors/financial_reports/annual_report_proxy_statement/ar_html/2011/index.htm#CS How I understand it is: supply/demand affect price of stock   negatively/positively, respectively. Correct. Volume is the amount of buying/selling activity in these stocks (more   volume = more fluctuation, right?). Sort of.  Higher volume means higher liquidity.  That is, a stock that is traded more is easier to trade.  It doesn't necessarily mean more fluctuation and in the real world, it often means that these are well-understood stocks with a high amount of analyst coverage.  This tends towards these stocks not being as volatile as smaller stocks with less liquidity. Company revenue (and profit) will help an investor predict company   growth. That is one factor in a stock price.  There are certain stocks that you would buy without them making a profit because their future revenue looks potentially explosive.  However, these stocks are very risky and are bubble-prone. If you're starting out in the share market, it's generally a good idea to invest in index funds (I am not a broker, my advice should not be taken as financial advice).  These funds aggregate risk by holding a lot of different companies.  Also, statistics have shown that over time, buying and holding index funds long term tends to dramatically outperform other investment strategies, particularly for people with low amounts of capital. I can often get the option at [a] price [between bid and ask] The keyword you use here is quite relevant: often. More realistically, it's going to be sometimes. And that's just how supply and demand should work.  The ask is where you know you can buy right away. If you don't wanna buy at ask, you can try and put a higer bid but you can only hope someone will take it before the price moves. If prices are moving up fast, you will have missed a chance if you gambled mid-spread. Having said that, the larger the spread is, the more you should work with limits mid-spread. You don't want to just take ask or bid with illiquid options. Make a calculation of the true value of the option (i.e. using the Black Scholes Model), then set your bid around there. Of course, if not only the option but also the underlying is illiquid, this all gets even more difficult. In short, yes. Implied volatility will capture any expected upcoming material announcements. There is also supply/demand impact bundled in which may inflate an option price, and by extension increase implied volatility. OTM and ITM options are particularly predisposed to this phenomenon -- which is of course at odds with the traditional BS model assumptions -- the result is referred to as the volatility smile. Implied volatility is quoted as an annualised measure but isn't necessarily an annual value -- it will correspond to the option time period. "At my soon to be legendary Stock Options Cafe, I recently wrote an article ""Betting On Apple at 9 to 2.""  It described a trade in which a 35% move in a stock over a fixed time (2 years) would result in a 354% gain in one's bet. In this case, the options serve to create remarkable leverage for speculators. In general, option help provide liquidity and extend the nature of the risk/reward curve.  There are option trades that range from conservative (e.g. a 'covered call') to wildly speculative, as the one I described above." "Yes, of course there have been studies on this.  This is no more than a question about whether the options are properly priced. (If properly priced, then your strategy will not make money on average before transaction costs and will lose once transaction costs are included.  If you could make money using your strategy, on average, then the market should - and generally will - make an adjustment in the option price to compensate.) The most famous studies on this were conducted by Black and Scholes and then by Merton. This work won the Nobel Prize in 1995. Although the Black-Scholes (or Black-Scholes-Merton) equation is so well known now that people may forget it, they didn't just sit down one day and write and equation that they thought was cool. They actually derived the equation based on market factors. Beyond this ""pioneering"" work, you've got at least two branches of study.  Academics have continued to study option pricing, including but not limited to revisions to the original Black-Scholes model, and hedge funds / large trading house have ""quants"" looking at this stuff all of the time.  The former, you could look up if you want. The latter will never see the light of day because it's proprietary. If you want specific references, I think that any textbook for a quantitative finance class would be a fine place to start.  I wouldn't be surprised if you actually find your strategy as part of a homework problem. This is not to say, by the way, that I don't think you can make money with this type of trade, but your strategy will need to include more information than you've outlined here.  Choosing which information and getting your hands on it in a timely manner will be the key." If you are the only one who puts in a large market buy order, then it would definitely push the price up. How much up would depend on how many would be willing to sell at what price point. It would also be possible that your trade will not get executed as there are no sellers. The same would be true if you put in a large sell order, with no buyers. The price would go down or trade not get executed as there aren't enough buyers. What it means is that the stock has already moved down. Options and other derivatives follow the price of the underlying they are not a precursor to what the underlying is going to do. In other words, the price of a derivative is derived from the underlying. "In a sense, yes. There's a view in Yahoo Finance that looks like this   For this particular stock, a market order for 3000 shares (not even $4000, this is a reasonably small figure) will move the stock past $1.34, more than a 3% move.  Say, on the Ask side there are 100,000 shares, all with $10 ask. It would take a lot of orders to purchase all these shares, so for a while, the price may stay right at $10, or a bit lower if there are those willing to sell lower.  But, say that side showed $10 1000, $10.25 500, $10.50 1000. Now, the volume is so low that if I decided I wanted shares at any price, my order, a market order will actually drive the market price right up to $10.50 if I buy 2500 shares ""market"".  You see, however, even though I'm a small trader, I drove the price up. But now that the price is $10.50 when I go to sell all 2500 at $10.50, there are no bids to pay that much, so the price the next trade will occur at isn't known yet. There may be bids at $10, with asking (me) at $10.50. No trades will happen until a seller takes the $10 bid or other buyers and sellers come in." Options pricing is based on the gap between strike and the current market, and volatility. That's why the VIX, a commonly accepted volatility index, is actually just a weighted blend of S&P 500 future options prices.  A general rise in the price of options indicates people don't know whether it will go up or down next, and are therefore less willing to take that risk.  But your question is why everything underwater in the puts chain went higher, and that's simple: now that Apple's down, the probability of falling a few more points is higher. Especially since Apple has gone through some recent rough times, and stocks in general are seen as risky these days. Buying pressure means there are more interested buyers than there are ready sellers putting upward pressure on prices. That might include institutional buyers who are slowly executing buy orders because they still want the best prices possible without clearing out the market. Buying pressure doesn't have to be related to volume at all. If everyone who owns shares think they are going to be worth far more than recent market prices, they will not offer them for sale. That means there is more demand to buy than there is a supply of shares to be bought. That condition can exist regardless of trading volume.