Metallicity (Z) trends of the OBe star fraction. Top panel: in the low-Z regime, we show the galaxy-wide OBe star fraction calculated in this work in the absolute magnitude interval −3 > M_abs > −5 with large diamonds. Bottom panel: literature studies of stellar subsamples within different galaxies, which targeted cluster and/or field stars: K99 (Keller et al. 1999), M99 (Maeder et al. 1999), M05 (McSwain & Gies 2005), W06 (Wisniewski & Bjorkman 2006), I13 (Iqbal & Keller 2013), Bonanos (Bonanos et al. 2009, 2010), P20 (Peters et al. 2020), and ZB97 (Zorec & Briot 1997). We only show clusters with 20 or more OB+OBe stars, and we do not show multiple measurements for any cluster. In K99, M99, M05, W06, I13, and P20, narrow-band photometry was used to identify OBe stars. For a part of the sample in M99, OBe stars were identified with spectroscopy. Bonanos used IR excess of stars with known spectral types to identify OBe stars. ZB97 used a sample of stars with known spectral types. For reference, we show the results of this work again with a dotted line. The metallicities in Holmberg I and II (Ho I and II) are estimated using oxygen abundances (Croxall et al. 2009). The two highest-metallicity galaxies are our own Milky Way (MW) and Andromeda (M 31). For Z_MW, we adopt the Solar metallicity, and we adopt Z_M31 = 1.5 Z_⊙ from P20.