When being transported by pipeline, natural gas is often emitted to the atmosphere, either for depressurization (venting emissions) or leak through the pipeline (fugitive emission). The emission level must be well estimated to provide relevant informations and recommendation to formulate strategies for reducing greenhouse gas (GHG) emission. Organizations such as INGAA (The Interstate Natural Gas Association of America) and IPCC (Intergovernmental Panel on Climate Change) provide GHG estimation guidelines which are adopted by many companies and countries. This study estimates the emission level of a natural gas pipeline in West Java using emission factors referring to INGAA and IPCC guidelines with flow rate variation. The result shows that the flow rate variation affects the total emission based on Tier 2 and Tier 3 INGAA as well as Tier 1 IPCC. It is also shown that fugitive emissions dominate the total emission of gas pipeline. However, the use of different methodologies and guidelines gives different emission level for the same pipeline. Different estimation results of emission level have been reviewed and national emission factors database for gas transmission is highly suggested to be developed. © Published under licence by IOP Publishing Ltd.