With the growing number of horizontal holes being drilled, petroleum geologists must handle increasing amounts of material having greater lateral than vertical extent. This requires novel techniques in description, interpretation, and data manipulation. This paper describes the core handling and descriptive techniques used for a heterogeneous 28.6 m horizontal core from the eolian Rotliegende reservoir of the Barque gas field in the United Kingdom southern North Sea. The core is subparallel to structural dip, slowly cutting down stratigraphically but sampling only a limited extent (laterally or vertically) of the reservoir. One facies boundary can be traced for about 12 m along the core, and for a significant proportion of the core, two facies with markedly different rese voir properties occur across the same 10-cm core diameter. The core is unrepresentative of the reservoir, as described from vertical wells, in two ways: the overall lithofacies composition in the core is comparatively biased toward poor-quality (water-laid) facies, and the presence of a thin cemented layer in the normally better quality (eolian) facies markedly decreases their average porosity/permeability. Care must be taken in extrapolating plug data from the core to field models. Apparently, contradictory wireline responses are explained (through calibration to the core and by consideration of the physical basis of petrophysical log responses), allowing the construction of facies models covering the formation around the borehole.