The ability to detect neutrons from the spontaneous fission of U-238 in samples of depleted uranium with organic liquid scintillation detectors is presented. In this paper we introduce a small modular organic liquid scintillator detector array that can detect changes in mass of U-238 between 3.69 g and 14.46 g. To do this, 18-h assays of various masses of 0.3% wt. of depleted uranium dioxide were assessed using four EJ-309 detectors, a mixed field analyser operated in pulse gradient analysis mode, and associated counting components. We observe a background-corrected fast neutron count sensitivity of (2.0 +/- 0.3) x 10(-4) n g(-1) s(-1) per detector. This research demonstrates a proof of concept for depleted uranium quantity to be assessed passively on a non-intrusive basis via its spontaneous fission decay.