Once the scopes are defined, the next step would be choosing appropriate emission factors to convert energy use into corresponding greenhouse gas emissions. For gas and diesel, there are readily available standard emission factors to be used. But emissions from the use of electricity clearly depend on the fuel mix and efficiency of the power plants. This renders the conversion factors vary from country to country and also change over time. International Energy Agency has estimated country specific emission factors including those for Singapore (both 1990 and 1996 values). They were calculated by dividing total CO2 emissions from electricity generation with total electricity produced, including electricity from nuclear power and renewable (Thomas et al., 2000). Nevertheless, the fact that Singapore’s power generation industry has made significant progress both in fuel mix and efficiency makes it necessary to update the emission factors to reflect these changes. One of the strategies adopted by the Singapore government to reduce environmental impact from power generation is to switch from burning fuel oil to natural gas for power. During the last five years, the proportion of electricity generated by natural gas has increased dramatically from 19% to 74%. Besides, the use of more efficient technologies has improved the overall generation efficiency from 37% to 45% in the same period (NEA, 2006).