I havn't seen an oscar over 14", so any pictures would be good. I'm not doubting it, just a picture with a reference (ruler or similar). What I do doubt are claims of oscars at 16-18" (Until I see photos, then I will believe it)
Having said that I did find this source.
Oscar sampled from the creels had a mean length of 252 mm and a mean weight of 410 g. Fifty percent of the oscar anglers interviewed used artificial lures, while other anglers used either crickets, minnows, shrimp, worms, or cut-bait. The largest documented oscar caught in the Everglades weighed 790 g.
A 790 gram oscar must be some size, especially if a 25cm fish weighs an average of 410 grams. Note that is the 'wild' not aquarium conditions.