Market Share is an economic head-to-head game where players take the role of company owners specialising in producing and selling a product in a duopoly setting. Each economic quarter, the companies will hire experts, pick up contracts, and decide on advertising expenditure (that will shape the potential market share) and the amount of product to be produced. The demand, which is uncertain and affected by the outcome of random events, needs to be fulfilled from the current quarter's production but also excess production from previous quarters (inventory), converting potential market share into actual market share. Unfulfilled demand and unfulfilled contacts will lead to reduction of the company’s share value.
The game is played over 8 rounds (8 quarters or 2 years). At the end of the 8th round, each company owner sums up the wealth accumulated during the game (company cash, shares, value of inventory stock). The winner is the player with the most total wealth. However, an early finish is possible. The game may end before the end of the 8th round if one of the two companies has dominated the market or if a company goes bankrupt.