Until 216 vertical electrical Schlumberger soundings were made, little was known about the subsurface geology at the Wadi Surdud area in the coastal plain of the Yemen Arab Republic. These soundings provide information on the distribution of aquifers, aquitards, and impermeable rocks, and the salinity of the groundwater.A first, qualitative interpretation of the geoelectrical sounding curves gives a general impression of the hydrogeologic setting and the aquifer boundaries. However, a more detailed, quantitative interpretation shows that no single resistivity model completely satisfies all the hydrogeologic and geologic facts and theories. Basically, two different models are possible: in one the thickness of the aquifer is fixed; in the other, its resistivity is fixed. Several geologic and hydrogeologic hypotheses may be put forward to support each model, varying from relying upon tectonic events and sedimentary depositional environments to influences of agriculture and water abstraction. Both models are supported by the data. However, geophysical well logging in two exploratory boreholes provided conclusive evidence for the model in which the thickness of the aquifer was fixed.