Abstract:Basque has an apico-alveolar /s "/, a lamino-alveolar /s «/, and a prepalatal sibilant /S/ that are represented by the letters , , and , respectively. The apico-alveolar and the lamino-alveolar sibilants have merged in some areas of Biscay, Guipuzcoa, and the Basque-speaking territories of Alava (e.g., Hualde 2010), and Spanish has been hypothesized as a factor driving this merger (Jurado Noriega 2011). On the other hand, complex sibilant systems like the traditional Basque one tend to be neutralized independently of language contact (Bukmaier et al. 2014). In order to add to this debate and shed new light on the merger, this study explored Biscayan Basque, a variety at an advanced state of the merger (Hualde 2010). More precisely, the study tested how the degree of bilingualism affects the production of the sibilants under study and the resulting neutralization by performing an acoustic analysis of the data. The results show that Basque-and Spanish-dominant speakers behave differently with regard to the sibilant merger, and that they have different places of articulation for their sibilants. Only Basque-dominant speakers maintain a significant distinction in the place of articulation of and overall, whereas Spanish-dominant speakers do not make a distinction among sibilants. Furthermore, the resulting merged sibilant is less fronted for Spanish-dominant speakers than the sibilants of Basque-dominant speakers.