What is the most common blood type?

This is an average distribution of the blood types in the United States. The distribution may be different for specific ethnic groups: 

Blood Group / RH StatusPercentage 
O Positive (O +)38 %
O Negative (O -)7 %
A Positive (A +)34 %
A Negative (A -)6 %
B Positive (B +)9 %
B Negative (B -)2 %
AB Positive (AB +)3 %
AB Negative (AB -)1 %