|Abstract:||This article contributes to the understanding of gradient phonological patterns by investigating graded vowel co-occurrence in Oceanic languages. In particular, vowel co-occurrence patterns in disyllabic stems are investigated in four languages: Samoan, Tongan, Hawaiian, and Fijian, as well as reconstructed forms in Proto-Oceanic and Proto-Malayo-Polynesian. With some variation in degree, all languages exhibit an over-representation of identical vowel pairs (e.g., i-i), an under representation of similar vowel pairs (i-e), and no special restrictions on dissimilar vowel pairs (e.g., i-o). These graded restrictions are also subject to order effects in all languages because the dissimilar > similar inequality in frequency is only found in certain orders. Our focus is on documenting the patterns supporting these generalizations so that future theoretical analysis will rest on strong empirical ground. In addition, we propose one such analysis using gradient constraints on parasitic vowel harmony.