Energy experts project that global oil supplies will only meet demand until global oil production has peaked sometime between 2013 and 2020. Declining oil production after peak production will cause a global energy gap to develop, which will have to be bridged by unconventional and renewable energy sources. Nuclear, solar and hydrogen are destined to become major energy sources during the 21st century, but only if their enabling technologies improve significantly to ensure affordability and convenience of use. This paper will argue that global oil production will probably peak between 2004 and 2005, causing a serious energy gap to develop sometime between 2008 and 2010 rather than 2013-2020 as the energy experts projected. It will also argue that a transition from fossil fuels to renewable energy sources is inevitable. The paper will conclude, however, that fossil fuels with a growing contribution from nuclear energy, will still be supplying the major part of the global energy needs for most, perhaps all, of the 21st century. (C) 2003 Elsevier Science Ltd. All rights reserved.