強制添加生質能源政策是目前世界各國最廣爲採用以發展生質能源的政策之一，然而回顧其相關文獻，政策的理論基礎卻十分薄弱。本文之主要貢獻，即是建立一包含能源市場、能源作物市場以及能源外部性的理論模型，分析政府應如何制訂最適添加比，以及添加比如何影響生質能源與能源（糧食）作物價格，並探討當相關變數外生改變時，最適添加比應如何改變以維持社會福利極大。研究發現，在其他因素不變下，生質能源添加比的提高將造成均衡的生質能源與糧食價格提高，而國際化石能源價格提高則會造成均衡的生質能源與糧食價格降低。其次，當溫室氣體排放對於社會福利的損害程度很大時，若單位生質能源之溫室氣體排放量降低，政府應採取較高的添加比；但當國際化石能源價格提高時，對最適添加比的影響則是不確定。

The biofuel blend ratio policy is one of the most widely applied measures to develop bioenergy The theoretical basis of this policy is, however, very weak. The main contribution of this paper is to specify a theoretical model that considers the energy and agricultural feedstock markets and externalities from the consumption of energy. Other things equal, we find that an increase in the biofuel blend ratio increases the equilibrium prices of biofuel and feedstock; an increase in fossil fuel price, however, decreases the equilibrium prices of biofuel and feedstock. Furthermore, if the problem of the greenhouse effect is serious, the optimal blend ratio should be raised when the greenhouse gas reduction technology of biofuel improves. However, the optimal adjustment of blend ratio to an increase in fossil fuel prices internationally is indeterminate. It depends on the relative magnitudes of several competing effects-in particular the utility impact on consumers and the externality of energy use.