Aside from catching them in the wild, one of the best ways to get your hands on Pokemon in Pokemon Go is by hatching eggs. This process involves walking around in real life, reaching a certain amount of kilometers traveled before your egg is ready.
The only issue is that you have no idea what’s in the egg until it hatches, so you could end up with something somewhat rare, or you could end up with yet another Pidgey. Initially, it was unclear how this process worked and if the game selected Pokemon to give to you completely randomly, but now we have some data that shows which Pokemon are the most and least common.
The information comes from Nether Fable, a website that gathered their data based on user feedback. They found that for 2km eggs, Weedle is the most commonly-received Pokemon, followed by Pidgey and Caterpie. The rarest is Clefairy, as only a little over one percent of all 2km eggs will result in a Clefairy.
When it comes to 5km eggs, Ponyta is the most common, although this species is still only present in about five percent of 5km eggs. The rarest is Koffing, who will only show up about 0.3 percent of the time.
Finally, with 10km eggs, Eevee is by far the most common, birthed by about 17 percent of all 10km eggs. The least common is the regional Pokemon which vary depending on what area of the world you’re in, i.e. Kangaskhan, Tauros, Farfetch’d & Mr. Mime.
Via Nether Fable, here’s the full breakdown of the egg hatching possibilities in Pokemon Go: