Experiments were conducted to isolate effects of buoyancy in gas-jet diffusion flames undergoing transition by hydrodynamic instability of the fuel jet. The jet Reynolds number was kept below the critical value for turbulent pipe flow to ensure an initially laminar fuel jet. Fast-reacting, nonsooting hydrogen fuel was used to characterize flame properties by jet Reynolds number and jet Froude number, which were varied independently. The jet Froude number was controlled by varying burner diameter and operating pressure in an Earth-gravity facility and by varying gravitational acceleration in the 2.2-s drop tower. flame characteristics were obtained using rainbow schlieren deflectometry, a line-of-sight optical diagnostic technique. Results show significant effects of buoyancy on near-field structure and transition from laminar to turbulent flame. Data suggest that a buoyant transitional flame could become laminar in the absence of gravity.