On Blood types, here is a chart from the US. I am sure it plays to a large degree anywhere. So for folks with the harder to find blood types, you are desperately needed!!!

Blood is grouped into four types: A, B, AB, and O. Each type is also classified by an RH factor – either positive ( + ) or negative ( - ). When a blood transfusion is necessary, donor and patient blood must be compatible. If not, the patient’s body will react to the incompatible donor cells, leading to complications, maybe even death.

Your ABO blood grouping and Rh factor are inherited from your parents. Check the chart below to see what percentage of the population shares your ABO grouping.

O + 37% O- 6%
A+ 34% A- 6%
B+ 10% B- 2%
AB+ 4% AB- 1%

When you donate, United Blood Services will send you a card with your blood type. Whatever type you are, someone in the community can benefit from your blood donation. Donate today. You’ll feel terrific!

Possible Blood Transfusion Combinations
Type: Can be given to patients with type:

O+ >> O+, A+, B+, AB+
A+ >> A+, AB+
B+ >> B+, AB+
AB+ >> AB+

O- >> O+, A+, B+, AB+, O-, A-, B-, AB-
A- >> A+, AB+, A-, AB-
B- >> B+, AB+, B-, AB-
AB- >> AB+, AB-

Patients with Type: Can receive type:

O+ >> O+, O-
A+ >> O+, A+, O-, A-
B+ >> O+, B+, O-, B-
AB+ >> O+, A+, B+, AB+, O-, A-, B-, AB-

O- >> O-
A- >> O-, A-
B- >> O-, B-
AB- >> O-, A-, B-, AB-

Take from
http://www.unitedbloodservices.org/humanbloodtypes.html