Lolmarket has six different gems in it, which I will call Lv 1-6 and color from now on.
The way the price is decided is by something called demand. When a lot of imaginary people wants a type of gem, the price will raise. If nobody wants it, the demand will drop. You can see this here;

The demand has a chance to update (=change) randomly, and you can't control in what direction it will go nor provoke it happening.
The formula for how the demand changes looks like this;
Lv 1 green gem: random value between -2 and 2
Lv 2 red gem: random value between -3 and 3
Lv 3 purple gem: random value between -4 and 4
Lv 4 blue gem: random value between -5 and 5
Lv 5 yellow gem: random value between -6 and 6
Lv 6 white gem: random value between -7 and 7
You do have a chance to influence the demand a little bit though, which is done by buying "Lolmarket Control: Type 1/2" (1 or 2) on the second page of the features shop, in the shape of a green star. You can either raise (Type 2) or drop (Type 1) the demand on gems. Buying a lolmarket control will give a number between 0-19, plus or minus depending on which type you choose. There is a time limit of how often you can buy these, once you bought you have to wait for the lolmarket to update 10 times before it is available again. There is also a limit of how low or high a demand can get. The lowest a demand can be is - 40, and the highest is + 40. Although it can go above or below this temporarily, if you buy a control type (explanations below). Demand and price works like so that each time your lolmarket is updated, the price will get +X where X is the demand the gem has after the update. Confusing? It basically means if your demand was +35, but got upped to +40 and your gem was worth 1000, after the update it will be 1040. If instead of plus we would have had minus, it would now be worth 960.
The order of how this happens is;
1. Demand gets +/- value according to info above
2. Price gets added/subtracted with the demand
3. Demand is automatically changed to +/- 40, if it is still above or below it. This means the price can be added or subtracted with more than 40, but it will automatically be set to 40 after the update.
You can increase the max amount of gems you can hold by buying a "Lolmarket expansion". As you can see in the picture below, I have 50 as max. You start out with 10, and can increase it up to 60. The price for each additional gem slot increases with each purchase, so it gradually gets more and more expensive. You find the upgrade on the second page of the features shop in the shape of a green star.
You can see how many gems you have of each kind, and what your maximum is here;

As mentioned lolmarket has six different gems. The first one is the cheapest, and the last one is the most expensive. The *price range* of each gem works more or less like this;
Minimum price Lv*500
Maximum price Lv*2500
What you have to keep in mind is that this is the price you buy the gem for, and the selling price is always 94% of the buy price, which means you can not actually sell a lv 1 gem for 2500 but 2350. Also gems rarily reach the minimum or maximum, so you won’t see a gem for their exact minimum price or maximum price very often.
I find that following these guidelines are helpful;

What this image is supposed to help you with, is to give you an idea of how high or low a gem is “likely” to go (it can go higher and lower in some cases, but it tends to stay around those levels if you do not use control types). It’s not necessarily the most profitable to always follow these prices, as you can read under methods, but it gives you a generic idea of what you can expect them to reach. It is best if you study the prices yourself and get a feel for more or less how high/low you see them reach, but this can give you a hint to start working with.
There are several ways to go about the lolmarket and each person has their style. Some people will buy the demand-control in features shop, others will not. It is entirely up to you how you want to do, but here are some general tips of how to make a good profit:
Control type use;
1. If you see many of the gems have a very low demand, buy a control type 1 to keep them steadily going down. The lower price you buy the gem for, the more profit you can make eventually.
2. If you see the demand of gems you have is going up, buy a control type 2 to give it a boost and keep it going up.
NOTE: Generally if the demand is +/- 15, it is not much point to try influence them with lolmarket control, because it often happens that it decides to go up when you said down or the other way around making it a waste of money. Usually you get more effect for the coins if you focus on keeping it in the direction it's already going.
Buy/Sell “methods”
One strategy is to buy gems only when they are close to their minimum price, and wait until they happen to be at their max, or very high. This gives you the biggest profit per gem, but takes longer since they often take a while to get to min. or max. price. But if you don't want to pay attention all the time, this is one way to do it. Often helps to buy some control types to help them reach. This generally takes a lot of time, and I wouldn’t recommend it since the main important factor is demand (read below), but if you want to just kinda idle about and not pay much attention, buying the gems at their lowest rate always and then either sell at max price or whenever you check in on it and think the profit is good enough. Again, I would recommend the second “method” presented below.
This “method” requires that you keep a close eye on the demand, and buy gems that you see are on the rise. For example say you see a Lv 4 Blue gem at 6000 with demand +40. This gem is very likely to continue upwards, and can still be raised by another 2000 or so, so buying it could be a good idea. Doing this way you might not get as much for each gem, but it tends to take less time between buying and selling and that way you can spend the coins again on some other gem and keep making profit all the time. I wouldn’t recommend buying gems that are too close to their max price though, since you will make very little profit in the end and also risk the demand not quite wanting to stay up ending in you not making profit at all. Also this “method” is to sell off gems when the demand is going down, even if that might not be the best profit attainable. Why? Since the demand is down, the price will drop and it might take a very long time to go back up. It is probably going to serve you more to sell it and buy some other gem that is on the rise. Of course if you are really OCD and want to sell at max price, you can keep waiting, but in most cases you will get more profit by following the demand rather than the price.
The single most important thing though, is that you sell your gems WITH profit. Of course this is rather basic and obvious, but it doesn’t hurt to stress it one more time. How do you know you if are making a profit? You can see it here;

+X means you are going to get that much more for the gem than what you paid for it. For example if you paid 1000, and the gem now sells for 1500, the profit will say +500. Basically the profit is how much of the total sell price is additional to what you spent on it in the first place.
-X means the gem is worth less now than it was when you sold it, and it is a bad idea to sell it. Generally selling with minus is not a good idea, but if you want to then you can of course do so. At times you might want to sell a gem for less because you need the green coins to buy some other gem with bigger profit-possibilities, but I would not recommend doing this unless you are “experienced” and know the lolmarket well, and even so I’d think twice about it.
IMPORTANT NOTE ABOUT PROFIT!
The profit displayed in the lolmarket will be counted from the last gem you bought, which can cause some “trouble”. Assume you buy 5 lv 1 gems for 500 gc, sell price say 470. The profit will display -30. Later you check in on it and the buy price has raised to 1000, and the sell price is 940. The profit will show +500. If you buy a gem now, for 1000, the profit will instead show -60, cause that is what the last gem bought would indicate. It will still show this even if you sell off that last gem. To avoid getting confused and risking to lose profit, I would recommend that you don’t buy gems of the same type at different occasions.
*FOR A SHORTER VERSION LOLMARKET GUIDE* made by Randomthought31, look here: http://www.kongregate.com/forums/60-anti-idle-the-game/topics/134535-randoms-guide-no-1-lolmarket?page=1#posts-2939593
I hope there aren’t too many errors, feel free to tell me if something is wrong or if there is something I missed to add. Also if anyone knows the exact time between each control type purchase, I’d appreciate it if you share =)
Credit for helping goes to;
- GeneralYouri
- Draconi
- qlordz

