When Connecticut's two casinos opened in the early 90s, they did so by reaching an agreement with the State of Connecticut to pay the state 25 percent of their monthly slot revenues.

As a result, both Mohegan Sun and Foxwoods must report their total slot earnings to the state each month. In December 2010, Foxwoods earned $45 million on its slot machines, an increase of 1.2 percent over December 2009.

Mohegan Sun took in $53.5 million dollars in December slot revenue. That's a 6 percent decline over December 2009, according to The Day of New London.

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In reporting its numbers, Mohegan Sun actually revealed some interesting information some gamblers might want to pay attention to.

Overall in December, $673,412,991 went through Mohegan's slot machines. It's a staggering number, referred to as the handle, by casinos. But Mohegan Sun only kept 7.94 percent of that total amount. That means more than 92 percent went back to gamblers.

What may be even more valuable information to the millions of people who drop dollars into those ringing, buzzing and screeching machines is that Mohegan Sun also breaks down which machines actually give gamblers the best odds at winning.

The casino has 6,404 slot machines scattered throughout it's sprawling gaming floors, and as most gamblers know, you can toss your money into those machines in many different denominations. But what the casino's December numbers show is that some of the 'cheapest' slot machines, actually have the worst odds for patrons.

For example, Mohegan Sun kept 11 percent of all of the money that went into its penny slot machines, with 89 percent returned to the players. That must be why the casino has more penny slots, 2,532 machines, than any other type. Not surprisingly, the majority of Mohegan Sun's slot revenue comes from these penny slots. Nickel slot machines took 12 percent, and give back 88 percent in December.

On the other side of the scale, the casino's $2 slots kept just 2.03 percent of the money that went in, giving back just under 98 percent to gamblers. The best deal for players, if you can afford it, was the casino's $10 slot machines, which kept a minuscule 1.77 percent of the money put into them, returning 99.23 percent to those spending their hard-earned cash.

In the middle were the casino's quarter slots, which returned more than 91 percent of the money put in back to patrons, and the $1 machines gave back more than 93 percent to gamblers.

But for those who want to play those machines, their best bet may be to play Mohegan Sun's multi-denomination slots. Those are machines on which a player can choose to bet in different amounts. In December, they returned 95 percent of the money that went into them. So gamblers had better odds dumping quarters into a multi-denomination machine, than playing those same coins on the quarter slots.

How do Connecticut’s casinos stack up against casinos in other states?

Those of us who try our luck on the slots at Foxwoods or Mohegan Sun hope the next pull of the lever will be life changing. But what are the odds you’ll really walk away with cash?

Connecticut’s two tribal casinos rank in the middle of the pack in terms of slot payouts when compared with other states around the country.

According to the Connecticut Gaming Commission, Foxwoods' slot payout average is 91.85 percent. Mohegan Sun pays back at a rate of 91.71 percent. That means Connecticut has the eighth-highest payout rate of the 20 states requiring casinos to report.

The best payout percentage by state is in neighboring New York. The Empire State, with its nine reporting casinos, pays back 93.75 percent. Resorts World in Queens, New York, pays the highest returns, at 95.05 percent.

The second state by average is Nevada, at 93.54 percent. West Virginia is at the bottom of the list, with an average of 89.12 percent payback.

1. NEW YORK – 93.75 percent
2. NEVADA – 93.54 percent
3. COLORADO – 92.85 percent
4. MISSISSIPPI – 92.77 percent
5. FLORIDA – 92.46 percent
6. DELAWARE – 92.36 percent
7. **KENTUCKY– 92.06 percent
8. *CONNECTICUT – 91.77 percent
9. NEW JERSEY – 91.41 percent
10. SOUTH DAKOTA – 91.36 percent
11. ILLINOIS – 91.00 percent
12. RHODE ISLAND – 90.88 percent
13. LOUISIANA – 90.74 percent
14. INDIANA – 90.71 percent
15. IOWA – 90.69 percent
16. MAINE – 90.68 percent
17. MISSOURI – 90.64 percent
18. OHIO – 90.34 percent
19. PENNSYLVANIA – 90.16 percent
20. WEST VIRGINIA – 89.72 percent

Percentages for include slots, blackjack, keno and video poker unless otherwise noted.
*Only slot machines
**Historical Horse Wagering

It’s not an exact science. Most states include video poker, Keno and video blackjack in their percentages, which tend to give better odds. Connecticut is the only state to include only slots. States like Nevada and Louisiana report area averages, not individual casinos. Other states, like New York and Florida, exempt tribes from reporting.

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The NBC Connecticut Troubleshooters sorted through slot revenue reports submitted to gaming, lottery and racing commissions for all reporting states. The Troubleshooters found that the areas with more competition tend to pay out higher averages.

Also, the lower the denomination, the lower the payback. Penny slots at both Connecticut casinos pay lower than 90 percent and receive almost half the total money wagered. The highest payouts at Foxwoods are the multi-denomination machines. They pay out 95.77 percent. Mohegan Sun’s $10 machines return 96.96 percent.

Foxwoods: July 2014 - May 2015

• $0.01: 89.34 percent
• $0.02: 90.83 percent
• $0.05: 90.40 percent
• $0.25: 92.06 percent
• $0.50: 91.47 percent
• $1.00: 93.50 percent
• $2.00: 93.34 percent
• $5.00: 93.96 percent
• $10.00: 94.70 percent
• $25.00: 94.25 percent
• $100.00: 95.56 percent
• Multi-Denomination: 95.77 percent
• Total: 91.85 percent

Mohegan Sun: July 2014 - May 2015

• $0.0025: 85.84 percent
• $0.005: 85.45 percent
• $0.01: 88.93 percent
• $0.02: 89.21 percent
• $0.05: 88.39 percent
• $0.25: 91.64 percent
• $0.50: 91.94 percent
• $1.00: 93.04 percent
• $2.00: 96.62 percent
• $5.00: 93.82 percent
• $10.00: 96.96 percent
• $25.00: 95.38 percent
• $100.00: 93.85 percent
• Multi-Denomination: 95.19 percent
• Total: 91.71 percent

Mohegan Sun president Bobby Soper argues his casino is as competitive as any around the country. He points out the economy and amount of free play credits they give to entice bettors plays a big part in keeping them from being even higher on the list.

'There are certainly a higher percentage of penny machines and nickel machines than previous,' said Soper. 'That across the board, across the industry is going to drive hold percentage.'

This investigation comes at a time when Connecticut is exploring the option of allowing Foxwoods and Mohegan Sun to jointly operate a third state casino, off tribal land, north of Hartford.

Locations being considered include the Enfield Square Mall, the Bradley Off-Track Betting property in Windsor Locks and the former Showcase Cinemas property in East Windsor.

The legislature approved the right for tribes to consider proposals from towns willing to host a satellite casino. Soper expects its cost could save thousands of jobs in the state and cost close to $300 million. It will include slots, table games and a poker room.

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Soper hopes to see it as close to the Connecticut border as possible. Just 5 miles from the border, MGM is building a $1 billion resort casino in Springfield. A spokesman for MGM estimates its slot payouts will be in the mid-90 percent.

State Sen. John Kissel believes casino expansion is bad policy. He argues a casino in his area of North Central Connecticut will not stop people, especially high-end gamblers, from traveling to Springfield.

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'They’re aware of payouts and they’re going to travel,' said Kissel, a Republican from Enfield. 'If Massachusetts is better than Connecticut, all the high-end gamblers are going to Massachusetts and the people that are struggling to just make ends meet are going to end up in North Central Connecticut.'

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In Connecticut, the tribes are required to pay 25 percent of all slot revenue to the state. They don’t need to pay anything on table games. The state has received nearly $7 billion total since Mohegan Sun and Foxwoods opened in the 1990s.