This paper investigates the variable production of English homorganic /s/ + consonant onset clusters (sC) in the speech of Farsi native speakers learning English as a second language. The results of a Goldvarb analysis reveal that: (1) the proportion of [e]-epenthesis (an L1-based phenomenon) is higher after a word-final consonant or pause than after a vowel (in which case the sC cluster is resyllabified as two separate syllables, i.e., [Vs.CV]); (2) with increased L2 proficiency and in formal situations, the amount of epenthesis decreases, conforming with Major's (2001) Ontogeny Phylogeny Model; and (3) as observed in several studies of L1 acquisition, markedness involving continuancy (and not sonority) is better able to capture the variable patterns of sC production found in Farsi-English interlanguage.