Transformer oil jet fires in substations can lead to significant economic losses. An experiment was conducted to study the shape of these fires under different conditions. The flame temperature ranges from 600 K to 700 K, forming a cylinder shape. The heat release rate increases with flame height to the power of 2/5. When the Froude number is 1.5 × 106, the flame behavior changes from buoyancy to momentum control. Flame width grows as heat release rate increases, with a relationship of width to the power of 1/3. The flame volume is related to the 0.85 power of the heat release rate. These findings help improve the analysis and prevention of transformer oil jet fire accidents in substations.