This paper compares and evaluates fourteen contemporary forecasts of global supply of conventional oil and provides some observations on their relative plausibility. Despite the wide range of modelling approaches used and multiplicity of assumptions made, it is shown that forecasts can be usefully compared along two dimensions, namely: shape of future production profile and assumed or implied ultimately recoverable resource of conventional oil. Other differences between forecasts are either secondary or are components of these two parameters. The paper shows how large differences in the assumed size of the resource make relatively little difference to the timing of a global peak in conventional oil production. It also examines the impact of rates of discovery, reserves growth and depletion on the forecast date of peak and shows how forecasts that delay this peak until beyond 2030 rest on assumptions that are at best optimistic and at worst implausible. (C) 2010 Elsevier Ltd. All rights reserved.