Four experiments examined listeners' segmentation of ambiguous schwa-initial sequences (e.g., "a long" vs. "along") in casual speech, where acoustic cues can be unclear, possibly increasing reliance on contextual information to resolve the ambiguity. In Experiment 1, acoustic analyses of talkers' productions showed that the one-word and two-word versions were produced almost identically, regardless of the preceding sentential context (biased or neutral). These tokens were then used in three listening experiments, whose results confirmed the lack of local acoustic cues for disambiguating the interpretation, and the dominance of sentential context in parsing. Findings speak to the H&H theory of speech production (Lindblom, 1990), demonstrate that context alone guides parsing when acoustic cues to word boundaries are absent, and demonstrate how knowledge of how talkers speak can contribute to an understanding of how words are segmented. (Contains 3 figures.)