In 2010 we investigated the applicability of the current k0 and k0-fission factors for the determination of the n(235U)/n(238U) isotopic ratio in multi-elemental samples containing uranium. An overestimation 3–4 % was observed in our determinations when employing the recommended 2003 k0-literature. After a recalibration of all our laboratory instruments, a 3 % overestimation was still observed in this work when employing this nuclear data. Therefore we aimed at the experimental re-determination of these composite nuclear constants in order to enhance the reliability of the isotopic ratio determination method and the accuracy of our data-filtering algorithms. New k0- fission factors are given for 7 nuclides that are not currently present in the 2012 k0-database. Several additional k0 factors are introduced for some nuclides in this library. Our k0 results are also compared with those recently reported by Blaauw et al.