Mucin glycosylation and individual susceptibility to disease is linked to the In Situ microenvironment that determines features of the individual- and disease-specific glycans. In tissue culture paradigm, the In Situ environment is not recreated and the synthesis of signature glycans vanishes. To evaluate the impact of the in situ-specific gastric epithelial environment on mucin glycan synthesis we investigated gastric mucin collected from 36 individual rats subjected to the same conditions and diet. The secretion collected during 3 hours of gastric perfusion contained from 67.7 to 1096.6 nmol mucin glycans and from 42.0 to 245.8 nmol glycosphingolipids (GSL). We identified four groups, each consisting of 6 animals, that contained O-glycans interacting with apical epithelial mucin receptor comprised of N-acetylgalactosamine (GalNAc), galactose (Gal), N-acetylglucosamine (GlcNAc) and fucose (Fuc) in the ratio of 1:2:2:1, 1:2:3:1, 1:3:2:1, and 1:4:2:1. The remaining 10 rats produced glycans containing GalNAc, Gal, GlcNAc, Fuc in ratio 1:1:1:1, partially fucosylated glycans, and Fuc-free glycans consisting of GalNAc:Gal:GlcNAc in ratio of 1:4:2. The data support our hypothesis that individual-specific-gastric epithelial environment and individual-specific metabolome provide final imprint on the quantity, composition, and termination of mucin O-glycans.