In this fourth paper on the lithostratigraphy of Oligocene deposits in the province of Limburg, Belgium, an east-west section is described within the municipality of Borgloon. The following Tertiary units have been encountered: Neerrepen Sands, Atuatuca Formation, Berg Sands, Nucula Clay, Kerniel Sands. The sediments in this section show a slight dip in a westerly direction. A comparison with an east-west section at Tongeren demonstrates that rather important tectonical movements must have occurred. It has not yet been possible to connect the Oligocene deposits in the Tongeren-Borgloon region with those in the Leuven-Tienen area.