The number of ads potentially relevant to search query information may be increased by relaxing the notion of search query keyword matching. This may be done, for example, by expanding a set of ad request keywords to include both query keywords and related keywords. The scores of ads served pursuant to a relaxed notion of matching (those with keyword targeting criteria that matched words related to words in the search query, but not the words from the search query) may be discounted relative to the scores of ads served pursuant to a stricter notion of matching. This may be done by using a score modification parameter, such as an ad performance multiplier (when an ad score is a function of ad performance information) The score modification parameter may be updated to reflect observed performance data, such as that associated with {word-to-related word} mappings.