A method for determining electrical properties of a submarine petroleum fluid-bearing formation (1) under overburden geological layers (2) of thickness (s) under a seafloor (3) of a sea. The method includes:*arranging one or more transmitter antennas (9) in the sea, and arranging one or more electromagnetic receivers (8) in the sea, *the sea having a shallow sea depth (d) of 50-350 meters; *using the transmitter antenna (9) transmitting electromagnetic signals (10) of one or more pulses (11) having frequency of very low frequency between 0.01 Hz and 0.10 Hz; *using the receiver antennas (8) having an offset from the transmitter (9), for receiving propagated electro-magnetic signals (12) due to the emitted electromagnetic signals (10); *analyzing one or more components of the received signals (12) from receivers (8) having offsets between about 1 km and 12 km, whether the signals (12) differ significantly from a corresponding signal that would occur from a water-bearing formation (1), indicating a petroleum fluid-bearing formation (1).