A computerized system which implements a method for obtaining an improved set of relevant keywords from an initial set of relevant keywords and their associated relative ratings, utilizing the proven expertise and reliability of existing keyword expansion tools and the accumulated experience of search engines. The method comprises iterating over keyword seeds, search engines' results and keyword suggestion sources' results, merging lists of keywords and combining their scores by means of an optimization method and learned effectiveness of result sources. Keyword relevance scores may be effectively used to distribute a content provider's resources amongst keywords thereby to achieve inclusion and optimization in search engines' results. The system input is a set of one or more seed keywords and the system produces an expanded list of unique keywords, each keyword typically accompanied by a computed relevance score.