Void motion can be an important part of electromigration failure in interconnects. Investigating this process is difficult due to the large variation in behavior in identical samples tested under identical conditions. To deal with the large variability, we have tested 50 samples to failure at four different accelerated test conditions. Because our automated, in-situ technique images an entire test structure, the complete history of a test line is recorded. By testing many samples under direct observation, the complex motion of electromigration voids was comprehensively studied.