A fractal analysis method (rescaled-range analysis) was applied to wireline logs through the fluvio-deltaic Brent Group (Middle Jurassic) in the Dunlin field, northern North Sea, to test the applicability of fractal analysis in geological interpretation of subsurface data. This analysis reveals that the fractal dimensions of gamma-ray logs range from 1.0025 to 1.1033. A higher fractal dimension may indicate more heterogeneous lithologies or reservoirs. Analysis of the procedures adopted suggests, however that fractal concepts in wireline log analysis should be treated with caution. Changes in the calculation procedure can cause larger variations in the estimate of the fractal dimension for a single well than is seen between wells. The validity and suitability of fractals in geological wireline log analysis need to be considered carefully.