The traditional mechanical reel slot machine has one line across three reels. This middle payline in the oldest and most obvious payline. (Appeared when Charles Fey invented the slot machine in the early 1900’s.) Today these are usually $.25, $1 or $5+ games.

Machines were later developed with 3 lines on those same reels. These often have similar denoms to the single line games.

Some slightly more complex mechanical reel games have 5 lines on the same three reels. (Began in the 1970’s). Again, these are usually $.25, $1 or $5+ games as well.

Video slots initially had 8 lines or 9 lines in either a 3 reel or 5 reel format. (These began to appear in the 1980’s and the 1990’s.) These are often played in the nickel denomination.

Today’s video slots now have 15, 20, 25, 30 or even 100 lines. These are most often played in the penny denomination. Manufacturers are pushing more and more lines everyday becuase the Casinos want more lines which make more money.
So, how many winning lines should a slot machine have? A quarter denom should have 1-5, and nickel denom should have 8 or 9, and a penny should have 15 or more lines. It is all a matter of preference, but that is tha basic rule of thumb considering what most people play in Casinos across the the U.S.