01 november 2026

Charles Hall, Jean Laherrère, Roger Bentley, John Hallock, Dan Gowin

Abstract

This paper examines significant but largely under-recognised constraints to global oil supply. Global oil reserves are less than half the widely accepted value and have long been in decline. Moreover, as predicted, global production of conventional oil reached its essentially resource-limited maximum in 2005, and has been in decline since 2008. Thus since 2005 the marginal barrels of oil have been non-conventional oils and NGLs. This increased the production cost of oil, brought on oils with higher CO₂ emissions, and possibly lowered the overall net-energy of oil production. In addition, US oil production is likely to decline soon, and much of Middle East ‘spare capacity’ appears over-optimistic. Finally, if oil demand does not fall sufficiently, global production of even ‘all-liquids’ is forecast to become constrained around 2035. The paper explains why these constraints are not well known, and sets out the research required, including improving public-domain oil reserves data, and confirming that the decline in global conventional oil is essentially resource-limited. The latter requires detailed bottom-up assessment and modelling, or the use of public-domain data to estimate the global oil URR via Hubbert linearisation or Rystad Energy data, and applying the ‘mid-point’ rule. Research is also required into oil production costs by category, their CO₂ emissions and EROI ratios; Middle East and US oil supply; and global production of ‘all-liquids’. Finally, detailed quantitative research is needed on how oil price impacts economies, and on future global oil demand vs. supply to clarify what is possible in the energy transition.

See document on the editor website: 10.1016/j.energy.2026.141868. See pdf.

Until 09 november 2026, the document can be accessed free of charge on the following link.