This Master’s thesis is a comparative study of information retrieval results between three distinct search strategies in simulated automatic query expansion in a bibliographic database. Our purpose is to investigate which of the search strategies score the most effective precision and to what extent the same relevant documents are retrieved (overlapped). A thesaurus attached to the database is used to select appropriate descriptors for the baseline query formulations which subsequently are expanded with hierarchical relations. The search strategies are s1: A baseline query with two or three descriptors, s2: The baseline descriptors combined with at least one Narrower Term, s3: The baseline descriptors combined with Narrower Term and at least one Broader Term. A Document Cutoff Value of 15 is used and only the 15 highest ranked documents are judged by relevancy. The measurements used are precision for effectiveness and Jaccard’s index for overlap. In terms of precision, results reveal that s1 scores the highest value (average 84,8 %) with s2 and s3 in decreasing order (average 81,94 % and 61,41 % respectively). The overlap varies greatly depending on topic and the average is between s1 and s2 78,81 %, between s2 and s3 58,48 % and between s3 and s1 40,41 %. In short, average precision decreases as well as average overlap. The use of thesaurus in the applied strategy of automatic query expansion is not recommended in this specific database, if the aim is to increase precision. However, in single searches with the structure like s1 the thesaurus can be of assistance in the selection of specific search terms. / Uppsatsnivå: D