Oil reservoirs are generally described by its main characteristics including its lithology and the pressure-volume-temperature (PVT) data. In reservoir engineering calculations, PVT data are essential to determine the reservoir fluid composition and design the production facilities. PVT data of 10 petroleum crude wells of Tawke field- Zakho are investigated in the current study. The data were analyzed to define the mathematical models correlate and govern the reservoir fluids properties as a function of sulfur compounds in term of (H2S) evolved from the wells and dissolved in reservoir fluids. The results obtained showed that crude oils are classified as sour, and medium with high content of heavier fractions C6+ up to C14+ (average oAPI 23.4). The mathematical models explain the correlations were estimated. H2S evolved and dissolved in reservoir fluids proved to increase with increasing sample depth, reservoir pressure and temperature, gas oil ratio, coefficient of compressibility at reservoir pressure, and decreases with increasing oAPI, viscosity at reservoir pressure and bubble point pressure, and gross heating value.