在實務上，低品質廠商在接受高品質廠商的技術授權後，可能會同時生產高、低品質產品，亦即存在「多產品」的特性。本文建構一個垂直產品差異性模型，探討當存在此一特性時，授權廠商在不同授權契約下的市場均衡、社會福利以及其最適技術授權契約。本文的分析結果指出：在單位權利金授權下，被授權廠商會同時生產高、低品質兩種產品；但在固定權利金授權下，被授權廠商只會生產高品質產品。再者，當授權前兩產品的品質差異性程度較小（大）時，授權廠商偏好固定權利金授權（單位權利金授權）。此外，研究結果顯示，在兩部訂價授權下，不但會發生「多產品」的市場均衡，且其最適固定權利金與單位權利金均大於0。這些結果與「單一產品」（即假設被授權廠商只能生產高品質產品）下之結論迥異。

In practice, a low-quality licensee may continue to produce its low-quality product after receiving product licensing from a high-quality licensor. This paper assumes this is the case and constructs a vertically differentiated products model to investigate the optimal licensing contract and the resulting social welfare. We show that the licensee produces both the low-and high-quality products under royalty licensing; whereas only the high-quality product is produced under fixed-fee licensing. In addition, from the licensor’s perspective, fixed-fee licensing is superior (inferior) to royalty licensing if the quality difference between the two products is small (large). Finally, the optimal two-part tariff licensing by the licensor should consist of a positive royalty and a positive fixed fee and the licensee necessarily produce both products after licensing. These results are in sharp contrast to those in the licensing literature with the licensee producing only the high-quality product after licensing.