This thesis builds on previous taxonomies of lexical errors in order to find patterns of lexical errors in Norwegian intermediate and advanced English texts. This study uses a taxonomy created by Angela Hasselgren to determine patterns of lexical errors. Lexical errors are labeled by their routes (how the learner chooses the wrong word), effects (why the word is wrong) and influences (what causes the error). By locating and labeling lexical errors in two corpora, this study illustrates how lexical errors are distributed across texts written by Norwegian speakers of English. The distribution of errors uncovers patterns that in turn explain how and why some errors are repeated. By contrasting intermediate and advanced speakers, it is determined that the distributions of intermediate and advanced lexical errors are significantly different. The amount of errors is significantly smaller in the advanced texts. Comparative distributions show that intermediate and advanced learners have different ways of choosing words (routes), but the distribution of effects remains constant. Advanced learners appear to use direct L1-influence and intralingual influence more, while intermediate learners depend on indirect L1-influence.