Swelling elastomer seals and packers provide effective zonal isolation in difficult oil and gas fields, resulting in significant savings in rig time and development expenses. Companies involved in petroleum engineering applications provide no information about the longevity or endurance of swelling elastomer packers when exposed to different conditions in the well. This paper describes the design and construction of a test facility for long-term performance assessment of actual full-scale water and oil-swell packers, and the results of the 5-year study. The ten packers are made of three types of swelling elastomers, are kept in crude oil and saline solutions at room and high temperatures, and are exposed to varying high pressures. Regular logs of readings were maintained over the whole study period. Earlier sealing was observed in elastomers immersed in low-salinity water and subjected to high temperature. Rate of swelling was higher in water-based elastomers than in oil-based seals. One packer never sealed completely. Pressurized tubes either retained sealing the whole time or re-sealed after removing of pressure or reducing it to a lower value. Results for the fast-swell and medium-swell elastomer, low- and high-salinity water and crude oil, and low- and high-operating temperatures were mostly in line with short-term tests on laboratory samples published earlier. This unique longevity assessment study can be used by drilling engineers and developers in assessing the suitability of swelling elastomers for target fields and in improving the design of swell packers.