A simple high-performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) method was validated to determine the galactooligosaccharide (GOS) content of 14 commercially available fermented milks (yogurts, yogurts containing bifidobacteria, and ready-to-drink yogurts containing Lactobacillus casei) marketed in Spain. The repeatability of the method, expressed in relative standard deviation percentages, proved to be in the range 2.8-6.2%. The recovery percentages of GOS varied between 92.7% and 96.4%. The obtained results support the suitability of the method. The diversity of oligosaccharides content and their distribution profiles in commercial samples was investigated. The components identified in commercial fermented milks were d-Galp-β(1→3)-d-Gal (3-galactobiose), d-Galp-β(1→6)-Lac (6′-galactosyl-lactose), d-Galp-β(1→3)-d-Glc (3-galactosyl-glucose), and d-Galp-β(1→3)-Lac (3′-galactosyl-lactose). Individual GOS content showed a wide variation among fermented milks analysed. Commercial yogurts containing bifidobacteria showed higher amounts of GOS (0.36-0.58%) than ready-to-drink yogurts containing L. casei (0.29-0.44%) and traditional yogurts (0.22-0.25%). The total and individual GOS content remained significantly unchangeable (P≤0.05) after 21 d of storage at 4 °C in all analysed samples. Since GOS are recognised as prebiotic, information about their content in fermented milks would help to estimate the potential prebiotic activity of commercial products manufactured under different conditions. © 2008 Elsevier Inc. All rights reserved.