The flame holding and blowoff characteristics of bluff body stabilized premixed flames were studied in a rectangular duct with a triangular flame holder in the midspan of the duct cross section. Lean blowoff was first investigated at unvitiated and uniformly mixed flow conditions in order to characterize the baseline flame behavior and compare it with data from the literature. The lean blowoff margin was then characterized with upstream air vitiated at equivalence ratios of 0.15 and 0.33, without and with cooling, respectively. Further studies were performed with non-uniform fuel profiles (rich or lean in the center or asymmetric), thus imposing single and double fuel gradients near the flame holder. Fuel profiles were characterized using laser induced acetone fluorescence. Transitional blowoff behavior was documented with measurements of CH chemiluminescence emissions from the wake as well as high-speed imaging of flame dynamics. Simultaneous PIV and OH PLIF measurements were taken at transitional fuel-air ratios to capture flame edge and aerodynamic behavior as blowoff was approached to determine the driving mechanisms of final blow off. Post processing of the flame images and flow field revealed the interaction between the velocity field and flame sheet.