magnetic method is very old way to explore for oil
with gravity , they were the main geophysical tools in 50th and 60th of 20th cent.
because of their very low resolution and their high error possibility , they are used to guide exploration by showing the presence of sedimentary basins and to roughly estimate the sedimentary thickness.
but it is impossible to use both methods in order to determine a structural trap or to check the extension of a reservoir