Highly explosive materials smuggled in sea land cargo containers are a security concern. An algorithm based on neutron and photon measurements during active neutron interrogation with 14.1 MeV neutrons was developed. The detection algorithm has now been evaluated for effectiveness over a wide range of explosive sizes, positions, and cargo configurations. Various sources of uncertainty were also studied. An estimate of the false positive and false negative rates was completed for various measurement conditions. Results showed that, although minimum detectable mass depends on the surrounding cargo, explosive position, and cargo configuration, 200 kg RDX could be reliably detected.