Is ONE PIECE episode 138 filler?
Filler Yes, episode 138 of ONE PIECE is filler.
#138
Whereabouts of the Island Treasure! Attack of the Zenny Pirates!
島のお宝の行方！ゼニィ海賊団出撃！
Aired 22 Dec 2002
Mochibayo compiled this list from MyAnimeList's labels, because MyAnimeList's episode data is not reaching us at the moment.