Query result caching is an important mechanism for search engine efficiency. In this study, we first review several query features that are used to determine the contents of a static result cache. Next, we introduce a new feature that more accurately represents the popularity of a query by measuring the stability of query frequency over a set of time intervals. Experimental results show that this new feature achieves hit ratios better than those of the previously proposed features. Categories and Subject Descriptors H.3.3 [Information Storage and Retrieval]: Information Search and Retrieval ? search process; H.3.4 [Information Storage and Retrieval]: Systems and Software ? Performance evaluation (efficiency and effectiveness). General Terms Performance, Experimentation. Keywords Search engine, static caching, query result caching.