Population and economic growth have continuously driven global energy demand. Six types of primary energy resources (coal, oil, natural gas, hydro, nuclear, and biomass) are the main sources of energy supply. Contrary to the general belief, the mix of these energy resources has not changed much over the last 50 years. Fossil fuels still account for more than 80% of the global energy supply. While there is an increasing pressure to substitute fossil fuels with renewables to address the global climate change problem, the share of renewables in the current global energy supply is around 1% only, if traditional biomass and large hydropower are excluded. Since economic growth is the primary driver of energy demand, developing countries will contribute more than the developed economies on the future growth of global energy demand. Unless major policy shifts are urgently implemented, fossil fuels will remain predominant in the global energy supply mix in the medium run (20–30 years), if not in the long run (> 30 years).