Stock Manipulation
Commodity Speculation is a subcategory of Betting and Bluffing, in which in-game money is bet on different commodities in hope that that particular commodity will become the most valuable as the game progresses. Often the values of the commodities are continually changing throughout the game, and the players buy and sell the commodities to make money off of their investment.
Commodity Speculation includes both Investment games in which players have some indirect control over asset values, but have a hard time hurting others without hurting themselves; and Collusion games, in which players have huge direct control in manipulating asset values, forcing players to help others and manage shifting alliances.