Senior thesis for the Bachelor of Science in the Department of Environmental Science, Oregon State University, Corvallis, Oregon. Major advisor was Dr. Sylvia Behrens Yamada.The prey consumption rates of two estuarine crab species were compared: the introduced Carcinus maenas and the native Cancer magister. Similar sized crabs of each species were placed into individual perforated plastic boxes and then placed in a seawater table. Each crab was offered 50 Mytilus trossulus mussels (15-25mm) per day for a total of 5 days. Every 24 hours the number of consumed and partially consumed mussels was recorded. Carcinus maenas and similar sized Cancer magister exhibited the same mean consumption rate. This study helps to predict where Carcinus maenas will fit into the hierarchy of Pacific Northwest crabs.