8192
The chance of finding a wild Shiny Pokmon is 1 in 8192. For those who are interested in why this happens, read on. When you encounter a wild Pokmon, there are four numbers randomly picked. One is your Trainer ID. One is your Trainer Secret ID. So only two random numbers are really picked randomly at the beginning of a wild Pokmon encounter. The other two are randomly determined at the beginning of the game and stay static. These random numbers range from 00000 to 65535, resulting in 65536 different number combinations. It was programmed into the game that if one of the randomly-picked numbers (not your ID or secret ID) is less than 8, the Pokmon is shiny. This is because of the bitwise function exclusive or. Since there are 8 possible numbers in the game which are below 8 (7, 6, 5, 4, 3, 2, 1, and 0) the chance of finding a shiny Pokmon is 8/65536, or 1/8192. Because of the four numbers, Shiny Pokmon are no longer determined by Individual Values, as they had been in Gold, Silver, and Crystal. Therefore, it is possible to have a shiny Pokmon with Maximum IVs.