We update a harmonization methodology previously developed in 2015 to facilitate comparisons of long-term global energy projections issued by the International Energy Agency, US Energy Information Administration, ExxonMobil, BP and the Organization of the Petroleum Exporting Countries. We continue to find important differences across outlooks in the primary energy units used, the assumed energy content of fossil fuels, the assumed efficiency of nuclear and renewable electricity conversion from primary energy, the categorization of biofuels, and the inclusion (or not) of traditional biomass. The exclusion of non-marketed traditional biomass from US EIA and BP estimates, for instance, yields estimates of global primary energy consumption that are 10–16 percent lower than for IEA, ExxonMobil and OPEC, which include these sources. Assumptions about the energy content of fossil fuels can vary by 1–12 percent in the data we examined, requiring significant downward adjustment of primary energy consumption estimates for natural gas for BP and US EIA, as well as liquids for US EIA, to make them comparable to IEA and OPEC. Conventions about primary energy conversion of renewables can alter primary energy estimates for these sources, ranging from a 65 percent decrease to a 153 percent increase for particular power sources. We also find that there are significant differences in historical data used in these outlooks, even when measured in fuel-specific physical units such as barrels, cubic meters, or tonnes. After taking additional account of these differences in historical data, our harmonization methodology brings estimates within 2 percent or less of one another for most fuels in the 2014 benchmark year we examine. We conclude that undertaking a harmonization process such as the one we describe is necessary to provide an accurate benchmark for comparing results across outlooks. Our identification of important sources of divergence in convention and historical data also highlights areas where institutions that produce outlooks may find opportunities for the identification of common assumptions and data improvement. Enhancing the comparability of different outlook scenarios developed yearly by the IEA, OPEC, industry and other key organizations will stimulate meaningful dialogue among stakeholders to the benefit of energy decisionmaking worldwide.