This method is designed to evaluate the coking propensity of synthetic ester-based aviation lubricants under two phase air-oil mist conditions as found in certain parts of a gas turbine engine, for instance, bearing chamber vent lines. Based on the results from round robin data in 2008–2009 from four laboratories, this method is currently intended to provide a comparison between lubricants as a research tool, it is not currently a satisfactory pass/fail test. At this juncture a reference oil may improve reproducibility (precision between laboratories), a formal precision statement will be given when there is satisfactory data and an agreed on, suitable reference oil if applicable.