Abstract: A system is provided for locating and delineating sea floor occurrences of petroleum seepage, achieved by apparatus for the detection of the resulting abnormal distribution of electrical potential within the affected sediments. The system uses an electrically insulating probe, deployed by steel cable from a ship, for the implantation of numerous electrodes within the sediment at depths between 60 cm and 5 m. Insulated conductors within the probe connect the electrodes to a reference electrode by way of an electrometer which facilitates measurement of the difference in electrical potential between any one of the probe electrodes and the reference electrode. Digital measurements are conducted to an associated acoustic modem and thence to the ship through the water. The system allows rapid assessments of sedimentary electrical conditions over large areas of seafloor by the repeated introduction, utilization, withdrawal, and relocation of the probe.