Hope this is useful information I use it alot for College football. I only use this on College no thing else.

A parlay is a bet where two or more teams are involved; all of
which must win or tie. The more teams you choose to parlay the
better the payout. You can combine different sports point spreads
and money-lines in win/loss and/or totals betting. This is all
according to the rules of the BM’s that you are playing with. You
should always know the rules of the BM that you are betting with.
However, not all bookies have the same rules. All you have to do is
ask the BM what his house rules are, and he or she will be glad to
explain their rules to you. Be sure to write the rules down for later
reference..

Example: In the Chicago-Detroit game, the line is Bears –3.5 and
the total is 36. Parlaying a side and the total gives us four
combinations:



Bears -3.5 and Over 36
Bears -3.5 and Under 36
Detroit +3.5 and Under 36
Detroit +3.5 and Over 36

The odds of any one of these plays being a winner are 1-in-4, so
the actual odds are 3/1. Most books pay 2.6/1 (you may see it
written as 13/5) if both bets are at standard payoffs (-110).
Let's assume four different players each bet exactly $100 on a
different one of the four possible parlays for the above game. The
house would collect $400 in handle, collect $300 and pay out
$260 for a net gain of $40, which is a 10% theoretical hold (300260=
40, 40/400=10%).

Below is a chart showing the actual odds, standard payouts, and
the house Edge:

No. of Actual Standard House Edge

Teams Odds Payout
2 3/1 2.6/1 10.00%
3 7/1 6/1 12.50%
4 15/1 12/1 18.75%
5 31/1 25/1 18.75%
6 63/1 35/1 43.75%
7 127/1 75/1 40.63%
8 255/1 100/1 60.55%
9 511/1 150/1 70.51%
10 1023/1 300/1 70.61%

It doesn't take a Genius to see that parlays involving more than
three teams will do very well for the BM’s; however; it is hard for
bookmakers to split the action on multiple games. Therefore, the
higher juice is charged to cover the risk of having to pay out the
occasional large bet.

Good Stuff, so have you made any real roll on your parlays?
I try to stay away from those as most pro gamblers would be ecstatic with 50% or more wins.
So when you have to consistently win 3 or 4 games, it is nearly impossible to sustain and a good strategy to go broke. I bet maybe a combination of games straight up if the spreads are to high.

One thing people need to remember is that you should not get carried away with parleys. Alot of people like to play parleys because of the high amount of money you can win, however there's a reason it's high, because of the odds.

Best advice for me is that you don't do more then 4 team parleys.

Yeah and you better hope that 3 out of 4 are all but sure things, I have never lost a two team parlay, but the three team combo's are a killer. I am not going to resort to more and more games, as that is just wanting to lose in my mind. You will use all your luck just to lose your last game by one, believe me.

You write that most Pro Betters would be happy with 50% winners. Because of the house edge, just to break even you have to hit 54% of your straight bets.