We have applied an optimality approach to explore the interlanguage variation in the acquisition of English (L2) by native speakers of Spanish (L1). More accurately, we have focused on the phenomenon of vocalic epenthesis found in the realization of the syllable onsets s + consonant. Following Boersma and Hayes (2001), we have used the gradual learning algorithm in combination with the variation model proposed in Cutillas (2004). The results of our analysis for two Spanish female speakers show that the restrictions (as strictness bands) of their respective grammar systems overlap. We suggest some possible explanations for these results.