Never underestimate the value of pennies -- or at least, of nickels, dimes and quarters. For casino operators, fortunes are built on pocket change. From 2001 to 2002, enough people wandered into Mohegan Sun and started pouring change into the video games and slot machines to add up to an astonishing eight billion dollars. (This doesnt even take into account the money spent at table games, such as craps and baccarat.) At Foxwoods during the same year, the tally was closer to ten billion. After subtracting the amount returned to players in wins and the amount transferred to the states General Fund, the two casinos were left with a little more than a billion dollars in change, reports the Connecticut Division of Special Revenue.

Obviously, the casinos are doing pretty well for themselves, and the machines are the main reason. A survey commissioned by the giant casino operator Harrahs in 2003 showed that video poker and slot machines comprise nearly three-quarters of all casino games played in the United States. But while casino gambling in general, and the slots in particular, offer players a negative return on their investment, there are indeed better and worse machines to play.

When it comes to machines, the name of the game, so to speak, is in what are called "return percentages." Return percentage (called the theoretical payout in Connecticut) refers to the maximum amount per dollar that a casino pays out when measured over the long term. In other words, a return percentage of 95 means that, over a period of time, the casino pays out 95 cents per dollar played and keeps the other five cents.

While gambling is highly regulated, there is no national gaming board. The 11 states that give out commercial gaming licenses regulate the industry themselves, taking a share of revenues. Once casinos meet or exceed a legal minimum set by the states -- in Nevada,  its a mere 75 percent, and in Connecticut, its 80 percent -- then its game on. Since no one would play if the returns were really that abysmal, casinos have mastered the art of offering the minimum returns possible while still attracting those billions of dollars. In fiscal year 2002-03, Foxwoods had an average return percentage of 91.80, while during the same year Mohegan Sun came in at an average of 92.02, according to the Connecticut Division of Special Revenue.

These numbers vary not only month to month but also place to place. In Las Vegas, for example, the smaller casinos, off the beaten path and away from the major resorts, offer the best return percentages. Indeed, according to statistics supplied by the Nevada Gaming Control Board, the difference between returns on 25 cent slot machines located on the strip in Las Vegas versus those on the northern side of town (which is not a tourist destination) rings in at just over four percent.    

Because the Nevada Gaming Control Board only calculates return percentages for geographic areas rather than for specific casinos, theres really no way to know individual casinos return percentages in Las Vegas -- unless you're as committed to finding out as Michael Shackleford. A few years ago, this former government actuary turned self-employed gaming consultant conducted an intensive on-site study of Las Vegas casino slot machines. In other words, he played nickel machines at dozens of casinos and kept meticulous notes on his results. He found rates varying from a high of 93.42 percent (at the Palms) to a low of 85.02 percent (at the airport). His complete results are posted on his website, wizardofodds.com. (These numbers wouldnt apply to slots that take quarters or dollars.)

Things get even more complicated if you're trying to compare return percentages on different games (say, slots versus craps), and it just might take a degree from the Massachusetts Institute of Technology to fully fathom the statistical differences. Still, while clearly all slot machines are not created equal, Shackleford has one primary tip for playing the slots: Don't.

"Slots are a very bad bet," he says. "I wouldn't ever play the slots, even at the best casinos." He tries to direct people toward video poker instead, "which offers a much better bet." He suggests if you do go in for video poker, you should study strategies before you play; see his website for resources if you want to learn more.

But if  youre one of the people contributing to that billion dollar bottom line for the casinos, and losing doesnt bother you, Shackleford and the website slotsadvisor.com have some tips for playing the slots to help you win -- or, more realistically, to help you minimize your losses:

Play the maximum number of coins. If you want to stick with one coin at a time, it is better to play one quarter than three nickels. This is because casinos generally increase the return percentage as the coinage goes up. For example, according to the Connecticut Division of Special Revenue, in fiscal year 2002-03, five cent slots at Mohegan Sun offered a mere 86.58 return percentage, while the five dollar slots were at a much better 94.61.  

Never leave or play a machine that owes you money. Sometimes a machine will run out of money before it is finished paying off. If you get up, someone else can sit at your machine and claim they hit the jackpot - which was really yours.

Stay away from machines in places where the expectation is that most gamblers are "transients" - at the airport, for example. Also, while some specialists believe slots closest to the casino door offer the lowest return percentages, Shackleford found that in most cases, this  wasn't true. In other words, if one nickel machine had a certain return, then all others like it, regardless of their placement in the casino, returned the same percent.

Check out frequent player programs run by casinos -- if you don't mind getting on mailing lists. The more money you spend, the  more points you acquire, which you can cash in for rooms, meals, merchandise, and shows.

Decide on your primary goal before your start to play. Is it to play for three hours? Not to lose more than a hundred bucks?

Stop when you've reached your goal.