Red blood cells or erythrocytes are most abundant blood cells in the human body. They contain hemoglobin which has a high affinity for oxygen which the body needs for effective functioning. The average male human has 12 pints of blood with 4 to 5 pints of them as RBC. The average female has 9 pints. For more info, visit http://www.hematology.org/Patients/Blood-Basics/5222.aspx.