Deriving EROI for Thirty Large Oil Companies Using the CO2 Proxy from 1999 to 2018

Energy Return on Investment (EROI, sometimes EROEI) is one of the most important indices for evaluating the efficacy of a primary energy source. It is generally defined as the relation between the energy extracted from a given resource and the energy costs diverted from society to extract it. In this paper, the EROI of 30 oil companies was calculated using the CO2 emitted by the companies and declared in Sustainability and/or Annual Reports as required by law, to estimate the energy used for the production process over a time span of 20 years (1999-2018). The resulting EROI estimates for the companies analyzed are rather homogeneous and, except in some cases, these values are relatively constant over time. These values agree (although sometimes somewhat lower than) estimates derived by other methods.