Chase Cards aren't inserted into packs as frequently as Base Cards and can be enhanced with foil, shaped differently to normal Cards, printed on different material, or any combination of these things. Roughly speaking, (as odds are never guaranteed by Manufacturers), if you were to open 40 packs of Cards, you would usually get somewhere between 3 and 6 Chase Cards.
To confuse things further, there is always more than one type of Chase Card to find. These Chase Cards form smaller sub-sets of Cards within the main set, (usually 1 x 9 Card set and 1 x 6 Card set), and each one will focus on a certain aspect of the subject in more detail.
All of our Chase Sets are supplied already loaded into Ultra Pro (Platinum) 9 Pocket Pages, for ease of storage and viewing, and to ensure they're kept in top condition.