Copyright 2006 Steve Fransisco

A casino slot machine is one of the most popular casino games. Traditional slot machines are coin-operated machines with three or more reels. They spin when a lever on the side of the machine is pulled. The machines include a currency detector that validates the coin or the cash inserted to play. The machine typically pays off based on patterns of symbols visible on the front of the machine when it stops. Modern computer technology has resulted in many variations on the slot machine concept. Currently casino slot machines are the most attracting gambling method in casinos and they generate about 70% of the average casino's revenue.

A person playing a casino slot machine purchases the right to play by inserting coins or cash, into a designated slot on the machine. The machine is then activated by means of a lever or button. The game itself may or may not involve skill on the player's partor it may create the illusion of involving skill without actually being anything else than a game of chance. The object of the game is to win money from the machine. The game usually involves matching symbols, either on mechanical reels that spin and stop to reveal one or several symbols, or on a video screen. The symbols are usually brightly colored and easily recognizable, such as images of fruits, and simple shapes such as bells, diamonds, or hearts.

Most games have a variety of winning combinations of symbols displayed on the machine. If a player matches a combination as per the game rule then the slot machine pays the player cash or some extra games. Casino slot machines are programmed to pay out as winnings between 82 to 98 percent of the total waged money. The minimum payout percentage varies among jurisdictions and is typically established by law or regulation. For example, the minimum payout percentage in Nevada is 75 percent and 83 percent in New Jersey. The winning patterns on slot machines and the frequency at which they appear are carefully selected to deliver a certain percentage of the cost of play to the "house" (the operator of the slot machine), while returning the rest to the player during play. Suppose that a certain casino slot machine costs $1 per spin. It can be calculated that over a sufficiently long period, such as 1,000,000 spins, that the machine will return an average of $950,000 to its players.

There is a probability factor to the placement of casino slot machines on the gaming floor, but the highest paying machines are not often placed in high-traffic areas. Typically, machines of similar payback percentages are grouped together, with 1% or less difference between the groups of machines.