18MS is an 18xx game set in Mississippi and Alabama, together with portions of adjoining states. Players invest in railroad companies in an effort to have the greatest net worth at the end of the game. This is determined by adding the cash holdings of the players to the value of the stocks each owns. The game consists of five Stock Rounds, where players buy and sell stock in the various companies, each of which is followed by two Operating Rounds, where the various companies operate by laying tracks, placing stations, and buying and running trains.