In thermal systems, energy is most often transferred using working fluids. However, in many cases, commonly used working fluids are limiting the effectiveness of present systems. For this reason, researchers are exploring nanofluids as a possible alternative to standard working fluids. Recent developments in nanofluidics have shown that hybrid nanofluids possess highly desirable properties for this application. Hence, this paper illustrates methods to optimize the thermal conductivity of hybrid nanofluids for implementation in heat transfer systems. Comparisons between independent experimental data are made to explore the effects of hybrid nanofluid characteristics on thermal conductivity. Characteristics of interest include the temperature, concentration, base fluid, surfactant, particle mixture ratio, particle sizes and materials, etc. Possible mechanisms of thermal conductivity enhancement are also discussed.