The present invention provides synthetic Pseudomonas aeruginosa lipooligosaccharide (LOS)-based oligosaccharides and conjugates containing various P. aeruginosa serotype-specific oligosaccharide antigens or various core P. aeruginosa oligosaccharide structures or motifs. The invention further provides P. aeruginosa LOS-based immunogenic and immunoprotective compositions and antibodies derived therefrom for diagnosing, treating, and preventing infections caused by P. aeruginosa.