This paper presents an approach to calculating the acoustic properties, i.e., sound speed, and scattering cross-section, of oil, oil/gas, and oil/gas/sea water mixtures. The petroleum industry characterizes reservoir fluid in terms of the relationship between pressure, volume and temperature (PVT) of the oil utilizing the formation volume factor (FVF), which is defined as the ratio of the volume of oil at a pressure and temperature relative to a stock tank barrel (STB) at surface conditions. Another important oil reservoir parameter is the gas-oil ratio (GOR), which is the percent by volume of gas which is present in the oil at reservoir conditions (the gas is typically entirely dissolved—i.e., none is free—due to the great pressure). The reservoir fluid is typically under-saturated, meaning more gas could be dissolved in the oil, were it present. As the oil rises to the surface, the pressure and temperature drop. Once they drop below the bubble point, gas begins to come out of solution. Also, if fluids (oil and gas) are released into the ocean, sea water will become mixed in with the well fluids. The interest here is in the acoustic properties of oil only, oil/gas and oil/gas/sea water mixtures. The approach is to calculate the density and compressibility of the constituents and from them predict the aggregate acoustic properties using mixture theory.