We study the process in which search engines with segmented indices serve queries. In particular, we investigate the number of result pages which search engines should prepare during the query processing phase. Search engine users have been observed to browse through very few pages of results for queries which they submit. This behavior of users suggests that prefetching many results upon processing an initial query is not efficient, since most of the prefetched results will not be requested by the user who initiated the search. However, a policy which abandons result prefetching in favor of retrieving just the first page of search results might not make optimal use of system resources as well. We argue that for a certain behavior of users, engines should prefetch a constant number of result pages per query. We define a concrete query processing model for search engines with segmented indices, and analyze the cost of such prefetching policies. Based on these costs, we show how to determine the constant which optimizes the prefetching policy. Our results are mostly applicable to local index partitions of the inverted files, but are also applicable to processing of short queries in global index architectures.