A series of experiments to test the Experimental Gas-Cooled Reactor (EGCR) fuel element concept was conducted in the Oak Ridge Research Reactor (ORR) and the Engineering Test Reactor (ETR). The elements tested were sintered UO2 fuel pellets contained in stainless steel tubing. Principal test variables were fuel pellet geometry, cladding temperature, and fuel burnup. After irradiation, the elements were examined for dimensional stability, integrity of the cladding, the fractional release of fission gas from the fuel, and any interactions between the fuel and the cladding. Some elements were subjected to unusual and extreme conditions of operation and others were not built to EGCR specifications. Such elements experienced three types of failure: 1) severe cladding fractures, 2) microscopic cladding defects, and 3) failures in associated components. Detailed examination of these experiments showed potential problems which may occur if EGCR fuel elements are operated outside design conditions.