Operational activities of gas pipelines are associated with potential hazards and risks that can potentially lead to pipeline failure, including failure of the gas distribution pipeline in existing buildings. Unfortunately, few studies on risk analysis of the gas distribution pipeline in existing buildings have been published. Therefore, this study was conducted to provide a reference for analyzing the risk of pipeline leakage caused by small-scale leakage, large-scale gas release, and gas pipeline rupture in existing buildings in Indonesia not designed for gas installation. The study was performed using the event tree analysis method. The methodology of this study was initiated by identifying the scenario of the case of small-scale leakage, large-scale gas release, or gas pipeline rupture. Then, pivotal events were identified, an event tree diagram was constructed, the event failure of each pivotal event was determined, and the probability value of the outcome risk was calculated. The risk was evaluated in terms of fire, casualties, and gas released. The results of this study showed the highest risk in each scenario which can result in fire, severe casualties, and light poisoning. The highest risk in the small-scale leak scenario had a probability value of 1.5 � 10-3. In the large-scale gas release scenario, the highest risk had a probability value to incur a fireball, severe casualties, and light gas poisoning of 6.0 � 10-4. In the gas pipeline rupture scenario, the highest risk had a probability value of fireball, severe casualties, and light poisoning of 7.0 � 10-4. The probability value of each risk was reduced by the installation of a gas detector and water sprinkler as a barrier. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.