There are several types of O-ring seals that are commonly used in various industries for sealing applications. The most common types include Nitrile, Viton, Silicone, EPDM, and Neoprene O-rings. Nitrile O-rings are resistant to oil and fuel, while Viton O-rings are suitable for high temperatures and chemicals. Silicone O-rings have excellent flexibility and temperature resistance, while EPDM O-rings are ideal for outdoor applications due to their weather resistance. Neoprene O-rings are known for their resistance to ozone and weathering.