Pressure loss coefficients were measured for 8 converging-concentric, 15 converging-eccentric, 8 diverging-concentric, and 15 diverging-eccentric flat oval transition fittings. All tests were performed in accordance with ASHRAE Standard 120-2008, Method of Testing to Determine Flow Resistance of HVAC Ducts and Fittings. Two pressure loss coefficient equations were developed, one for converging and a second for diverging fittings based on the experimental data. The loss coefficient data and the regressed equations will be added to the ASHRAE Duct Fitting Database, thus increasing the population of flat oval fittings.