SPEC/GPC's benchmark uses Quake II's "TIMEDEMO" function to time the playback of a number of different pre-recorded game sessions, which include both single and multi-player matches. Results are reported in frames per second. The benchmark requires that results submissions include screen captures from the game, so that visual quality can be assessed. Results can be reported for two different tests at four different screen resolutions: 640x480, 800x600, 1024x768 and 1280x960. Vendors must report results for both tests under a given resolution, but have the option to report numbers for whatever screen resolutions they choose.
SPEC/GPC's Quake II benchmark is fully endorsed by id software, the developer of Quake II. It is available for free downloading on this site.