Human: I'm a bit confused about the different types of scuba diving gear. Assistant: 
The main difference between open circuit and closed circuit scuba is in the breathing apparatus. Open circuit scuba uses a tank of compressed air, while closed circuit scuba uses a rebreather system that recycles exhaled air. In open circuit scuba, you must carry an additional supply of oxygen for your dive. Closed circuit scuba has a higher efficiency rate, meaning it can use less oxygen than open circuit equipment to stay underwater for longer periods of time.