A method and system are provided for selecting advertisements for presentation to a user in response to a user search query. The system may include a keyword server for parsing the user search query and an index server for receiving the parsed search query. The index server may include an index of advertising phrases and pre-filtering components for comparing index entries to the parsed user search query in order to discard non-matching index entries and locate matching entries. The pre-filtering components may include either a phrase length pre-filtering component or a word hash pre-filtering component. The system may additionally include a listing server for sorting through the matching entries located by the index server and further filtering the matching entries for retrieval and presentation to the user.