What is the rate of which you encounter pineco?

Question

I've been through most of the routes/locations and have ran through the tall grass a lot, but I haven't encountered one.

Comments

what game are you playing?

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If you're playing HGSS, you can't find Pineco in tall grass; you can only find it by headbutting trees.

Answer 1

GS: Headbutt at Azalea Town, Ilex Forest, Lake of Rage, Routes 26, 27, 34, 35, 36, 37, 38, 39: 30%
C: Headbutt at Ilex Forest, Lake of Rage, Routes 43, 26, 27, 32, 29, 30, 31, 34, 35, 36, 37, 38, 39: 30%
DPPt: tall grass on Eterna Forest, Routes 203, 204, 210 (South) and 229 with Emerald in GBA slot after visiting Pal Park: 8%
HGSS: Headbutt: 30%
BWBW2: tall grass on Route 16 during outbreak: 40%
source

Answer 2

This depends on which game you're playing. Here is a link to a list of all of the locations Pineco can be found with each route you click on showing you the encounter rate of every Pokemon found on that route.