Waterflooding is one of the most common secondary oil recovery methods because of its economic efficiency. In case where many injection wells contribute to the oil recovery process of a production well, contribution proportion will be an important parameter for management of water injection. Besides the well-known Interwell Tracer Tests using artificial tracers injected into the reservoir, the method of using partitioning organic compounds in crude oil as Natural Partitioning Interwell Tracers (NPITs) shows a great potential for evaluating the contribution proportion of injection wells in oil extraction process. The paper presents the research results to illustrate an idea of using NPITs for calculation of the contribution of injection wells to a production well in homogeneous single-layered reservoir on UTCHEM simulation data with Five-spot model and Direct-line model. The results showed that the calculated values of contribution proportion are different from modelling values between 1 - 2%.