Transon is correct......there are 3 most common 9mm on the Market today (14 diff from the past). 2 of them are 9x19 & another is 9x18....the 9x18 should be called 9mm Markov. The other 2 are 9mm Luger/Parabellum and the 9mm Auto.
If you find Parabellum or Luger market on it....that's what you want. Some guns will cycle 9mm auto ammo fine, some will not. All depends on there design. (Beretta 92 I think works ok with 9-auto)
here are some pictures from another website so you can physically see the differnce.
hope this helps you