The most common blood type is O+. This means that the person has type O blood and is Rh positive. The next most common blood type is A+. Type O- is the universal donor, meaning that it can be donated to people with any blood type. However, type O- blood is also in high demand because it is rare and can be used in emergency situations when the blood type of the person in need is unknown. It is important to note that different ethnicities and populations have different frequencies of different blood types, so the most common blood type can vary depending on the specific population being considered.