Due to the geographical location of Oman in an arid zone, agricultural production depends fully on irrigation. The traditional irrigation systems (Aflaj, sing. falaj) supply more than one third of water for agriculture. Falaj is defined in the context of this paper as a canal system which provides water for domestic and agricultural uses. Oman has 3,107 active Aflaj producing about 680 Mm3 of water per year. The main objective of this study was to estimate the irrigation performance of Aflaj in Oman. Falaj al-Dariz and al-Nujaid were chosen as case studies. Both Aflaj are located in an extremely arid environment, where the rainfall is low and evapotranspiration is high. The study utilized an approach to estimate the irrigation performance of Aflaj by considering the falaj as a single unit of irrigation. The irrigation demand/supply ratio (D/S) was used in the analysis as a tool of evaluation. Date palm, the dominant crop irrigated by Aflaj, was selected for the analysis. In falaj al-Dariz the date palms were slightly under irrigated on a yearly basis. On a monthly basis, in winter, the D/S was below 0.6 and in summer it was above 1.0. On the other hand, falaj al-Nujaid was supplying too much water than the date palms needed all round the year. In winter the D/S ratio was as low as 0.25. Even in summer, the D/S ratio did not much exceed 1.0.