Which is the most common blood type?

O positive is the most common blood type in the world, carried by roughly 35 to 40% of people globally, though the exact share varies by region. In parts of Latin America, O positive is carried by a majority of the population, while in some countries, such as Japan and Norway, A positive is more common. Blood types are defined by markers called antigens on the surface of red blood cells. The ABO system was discovered by the Austrian scientist Karl Landsteiner in 1901, work that earned him a Nobel Prize in 1930. The positive or negative part refers to the Rh factor, which Landsteiner and colleagues identified around 1940.