Subject inversion in French is usually considered to be optional (Le Bidois 1952; Kayne & Pollock 1978) and more costly than variants with preverbal subject. As the result of verb movement (Hulk & Pollock 2001), it is claimed to demand higher processing cost (Holmes & O’Regan 1981). However, some studies suggest that subject inversion in relative clauses may even be favoured by certain semantic or heaviness constraints (Fuchs 2006; Marandin 2011). In this paper, we take an empirical approach to this question. In our corpus study using the French Treebank described in Abeillé et al. (2019), we found that subject inversion in object relatives can be as frequent as cases without inversion. We also found that inversion is preferred with longer subjects and shorter and non-agentive verbs. This pattern was confirmed in an acceptability judgement experiment as well as in a self-paced reading experiment. Thus, object relatives with and without inversion are not merely stylistic variants (i.e. two equivalent syntactic ways of expressing one meaning), but are more or less preferred depending on their properties. Our results are compatible with semantic accounts of relative clause processing (Mak et al. 2006; Traxler et al. 2002).