It is well established that contraction, like many other reduced forms, occurs more frequently in spoken than in written language (Biber 1988; Tobin 1994; Tottie 1991; Yaeger-Dror et al. 2002). Nevertheless, contracted forms in written texts have received the bulk of attention in corpus studies, traditionally seen as indicators of register and interaction type (Westergren Axelsson 1998; Biber 1988; Kjellmer 1998; Tobin 1994; Tottie 1991; Yaeger-Dror et al. 2002). In this paper, I investigate contractions occurring in the spoken conversation component of the BNC, first comparing occurrences of full and contracted forms then, following Yaeger-Dror et al. (2002), specifically focussing on competing aux- vs. not-contraction in similar contexts. The current analysis confirms a clear preference for contracted forms over full forms in the spoken corpus and, in so doing, sets the stage for characterizing the variation between two contracted versions of the same full form, for example, there’s not vs. there isn’t. Such competing aux- vs. not-contractions (Hiller’s “Janus Kontraktionen”) in the conversation component of the corpus encourage a lexico-grammatical analysis (cf. Tagliamonte & Smith 2002) as opposed to one strictly based on register, dialect or interaction type. In this paper, aux- and not-contraction are shown to prefer different grammatical and lexical environments. An explanation for this phenomenon is offered based on collocational preferences instead.