The distribution of fossil fuel reserves and resources between different regions and deposits has strong implications for climate change economics and policy. The task of stabilising the atmosphere is intimately linked to the question of long-term energy supplies as conventional petroleum reserves deplete, notwithstanding debates about the scope for reserve extension through continued exploration and development. It suggests a supply-side component to complement the consumption orientation of existing climate policies: the task is to ensure that investment and innovation moves towards the 'low carbon frontier' instead of the 'high carbon frontier'. This also implies that the OPEC countries have little to fear about the long-run impact of climate change policy. The priority is to deter development of more carbon-intensive unconventional petroleum deposits and technologies, and to ensure that the existing trends to diversify power generation sources continue and extend more widely over time. Supply-side constraints will not solve the climate problem in themselves - but they make the task a lot easier, if the opportunities are taken.