Abstract The PNL/Borax log was designed as a replacement for temperature and radioactive tracer logs in identifying channels in the cement sheath surrounding the casing in production or injection wells. This isnl the only application of the log. Because of the correction for thermal neutron diffusion, it can be used to differentiate between a channel and other mechanisms of fluid movement, such as a leaking packer, leaking squeezed perforations, and gas migration under an impermeable barrier within the formation. These added capabilities can result in a better diagnosis of the well condition. With the downhole processes pinpointed, the proper kind of remedial wellwork can be recommended to optimize the performance of the well. The PNL/Borax log has been successfully used to diagnose channels (or lack of channels) in dozens of producers in Alaska's Prudhoe Bay oil field, and has been run with mixed results in injectors. It has also been used to successfully distinguish between leaking packers and channels. In addition, the borax tracer has been found to be safe to wellsite personnel, and can be produced back out of the formation to minimize impacts of future neutron logging operations. This paper presents the basic theory behind PNL/Borax logging and provides field examples of its use in producers and injectors.