This method employs two neutron logging tools with different spacings between the source and the detector or two detectors in the same tool at different spacings. The spacings usually differ by 6 to 10 in (15.24 to 25.4 cm). The long-spaced log is run slowly and with a large time constant so that its statistical variation is not excessive, for the counting rate is much lower than that of the regular-spaced log. This technique has proved to be a potent technique for discriminating gas sands from oil sands in Venezuela.