We present an analysis of register variation (i.e. conventionalized and socially recurring linguistic patterns of intra-individual speech behaviour) of filler particles in German spontaneous speech in contrasting situated interactions. In this study, we analyse intra- and inter-individual differences in the use of lexical type of filler particles and their phonetic realizations. Data was elicited with a novel method where participants talk to a video-taped interlocutor in a simulated tele-conference. This set-up allows us to systematically and consistently manipulate the experimental condition while eliciting laboratory induced differences in fine phonetic detail. We find evidence for register differences but also a high inter-individual variability.