Since its initial assignment to the Elasmosauridae, the relationships of Brancasaurus had been considered well supported, and it was recovered by O'Keefe's 2004 analysis and Franziska Großmann's 2007 analysis.
Od początkowego umieszczenia wśród elasmozaurydów obecność w tej rodzinie Brancasaurus uznawano za dobrze wspartą, co zachowała jaszcze analiza O'Keefe'a z 2004 i analiza Franziski Großmann z 2007.