This paper introduces the history matching process of commingled wells and demonstrates how to reduce the uncertainty of the vertical permeability ratio (kV/kH) by analyzing the production logging results of horizontal wells which have been used only for allocation through the evaluation of horizontal well performance. The field discussed in this paper is an offshore carbonate oil field located to the Northwest of Abu Dhabi. In this field, a lot of horizontal water injectors have been drilled and completed for the purpose of reservoir pressure maintenance. Historically, most of horizontal water injectors were completed as comingled injector covering two layers isolated by thick dense layers. Due to the complexity of the well and the difficulty of well monitoring, the well performance of these horizontal water injectors was not fully integrated into the model history matching process. The kV/kH ratio is one of the important parameters for analyzing fluid movements in carbonate oil reservoirs. Generally, the value obtained from core analysis results is utilized for reservoir simulation models. In this paper, the effectiveness of analyzing production logging results for commingle wells is introduced as a method for evaluating kV/kH on the simulation model. The end result can reduce uncertainties of kV/kH resulting from heterogeneity of carbonate reservoirs. It is confirmed that production logging results of commingle horizontal wells are valuable for evaluating kV/kH to be defined the simulation model. They can help to reduce the uncertainty in kV/kH, although there is not enough data for the history matching process.