This article reports on an introspective study that examined the effect of EFL learners' L2 reading proficiency on their L2 lexical inferencing while reading an English expository text. The knowledge sources and contextual cues they used in the process, the level of success they achieved, and their rate of learning and retention of the inferred target words are examined. A taxonomy of the knowledge sources used by the participants of the study and illustrative examples are presented. The findings of the study are discussed in light of previous research, and some pedagogical implications are suggested.