An activation well logging method and apparatus for identifying and measuring the presence of vanadium in earth formations surrounding a borehole. A well logging instrument including a source of neutrons is used to irradiate formations for a period of time sufficient to activate vanadium. The gamma radiation emanating from the irradiated formations are detected by a scintillation detector having output pulses directly proportional to the energies of the incident gamma rays. The output pulses having energies characteristic of the element vanadium are separated and counted to provide indication of any vanadium present in the irradiated formations.