Differences between AI difficulty levels

[samuraigg]

Apologies if this has been answered before, but after doing a quick search on the forums and browse through the manual I didn't see this answered.

At what difficulty level (if any) does the AI start getting cheats or bonuses over the player? I'm currently having a lot of fun playing a game with a bunch of normal AI players, but I might not want to bump up the difficulty if they start getting resource or other advantages at higher levels.