Abstract: Reservoir connectivity evaluation is vital for efficient development of oilfields, accurate understanding of reservoir connectivity will affect its reserves estimation, development strategy, and even decide the success or failure of oil and gas field development. The conventional methods for it include the sedimentary facies analysis, lithofacies analysis, formation pressure analysis and reservoir fluid compositional analysis. However, these methods have their uncertainties or limitations. In this paper, the strontium isotope residual salt analyses (SrRSA) methodology is introduced. This information from the cored well in Rumaila oilfield in Iraq are applied to analyzing the reservoir vertical and lateral connections, thus demonstrating that in Main Pay sandstone reservoir formation occurs the vertical disconnection. So this reservoir is divided into three sets of development sequences; the major Mishrif carbonate reservoir is good in lateral connectivity, its oil?water interface is controlled by structure; the potential Yamama reservoir is poor in lateral connectivity, and its oil?water relationship is complicated, the fluid distribution is controlled by lithology. The case study indicates that the SrRSA information is one of the most efficient and economical methods for deterministic evaluation of reservoir connectivity, and it is of great significance for references and widely application