The chemical tracer flow test (TFT) technique for two-phase mass flow rate measurement has been in use since 1992 and is now employed routinely in the major geothermal fields of 6 countries. There have been continuous refinements in the TFT process over time, including introduction of new vapor and liquid tracers, and upgraded tracer metering equipment. Since TFT is now used by many operators around the world, it is important to ensure that the technique is consistent and robust, and not site-specific or sensitive to small deviations in methodology. Comparative data are presented for some of the various tracers, including recent tests on alcohol tracers. These tests show sulfur hexafluoride (SF6) is the most versatile and accurate tracer for TFT steam measurements, while alcohol can be used in limited applications. Sodium benzoate remains the primary liquid-phase tracer, but recent tests using naphthalene sulfonic acids (NSA) look very promising. The SF6 and NSA tracers allow miniaturization of the tracer metering equipment, resulting in greater portability and lower cost.