As inventory levels reach a critical stage, Blood Assurance is appealing to the public for O negative blood donations. Those who donate will be entered for a chance to win a trip to Universal Studios.While just 6 percent of the donor population has O negative blood, it is the universal type that can be given to anyone in an emergency situation when the patient’s blood type is unknown.O negative donors who donate blood during November and December will be registered to win a trip for two to Universal Studios. During November, visitors with any blood type can register to win $1,000 for the 501(c)(3) charity of their choice.Donors who do not know their blood type are asked to donate regardless since whole blood donations will last 42 days.Three Blood Assurance blood drives are scheduled for McMinnville this month, including two this week.