Fossilization is said to be a distinctive characteristic of second language (L2) learning (Selinker, 1972, 1996; Han, 2004). It is the most pervasive among adult L2 learners (Han and Odlin, 2006). This linguistic phenomenon has been characterized by cessation of learning, even though the learner is exposed to frequent input. Based on the findings of the MA dissertation of the first researcher which is about ‘phonetic fossilization’ and where she conducted a longitudinal study, Han’s Selective Fossilization Hypothesis (SFL) is used to analyze the obtained fossilized phonetic errors in relation to L1 markedness and L2 robustness with a particular focus on fossilized vowel sounds. This is an analytical model for identifying both acquisitional and fossilizable linguistic features based on learners’ first language (L1) markedness and second language (L2) robustness. The article first gives an overview of the theory of Interlanguage and the phenomenon of fossilization. Then, it introduces SFL. This is an attempt to study fossilization scientifically. In other words, it tests the predictive power of a developed L1 Markedness and L2 Robustness rating scale based on Han’s (2009) model. The present study has pedagogic implications; it is an opportunity to raise teachers’ awareness on this common linguistic phenomenon.