A phylogenetic analysis of "Cetiosauriscus" was conducted in 2003 by Julia Heathcote and Upchurch, based upon the two most inclusive matrices of the time, those of Jeffrey A. Wilson (2002) and Upchurch (1995), neither of which had included the taxon in the past. Added to the analysis of Upchurch, "Cetiosauriscus" placed as the sister taxon of "Tehuelchesaurus", in a group including "Mamenchisaurus", "Omeisaurus" and "Euhelopus", and a placement within a group of "Omeisaurus" and "Mamenchisaurus" was also found by using the Wilson matrix. Based on these two results, Heathcote and Upchurch concluded "Cetiosauriscus" was not a diplodocid or even within Diplodocoidea, instead being a more basal sauropod outside Neosauropoda. The phylogenetic analysis of Rauhut "et al." (2005) resolved "Cetiosauriscus" in a clade with "Omeisaurus", itself in a group with "Losillasaurus" and "Mamenchisaurus", outside of Neosauropoda. The phylogenetic relationships of "Cetiosauriscus" were also tested in 2015 by Tschopp "et al.", as a potential diplodocid. Although the genus was found to be within Diplodocimorpha with one analysis method, it was also found outside Neosauropoda. In both, "Cetiosauriscus stewarti" was found to be in a clade alone with "Barosaurus affinis", a dubious species known only from foot bones. Tschopp "et al." concluded that "Cetiosauriscus" was not a diplodocid or a diplodocoid, as forcing it to be outside Neosauropoda was more parsimonious than forcing it to be within Diplodocoidea in all analyses. As the paper was only to test relationships within Diplodocidae, more solid conclusions regarding the position of "Cetiosauriscus" could not be made. The results of the favoured cladogram of Tschopp "et al." is shown below: