In the April 2019 issue, Liggio et al. published an analysis that utilized CO2 emission estimates obtained from aircraft flight studies carried out in the Athabasca Oil Sands area in northeastern Alberta in 20131. The authors reported significant differences between CO2 emission estimates from their aircraft flight studies compared to the industry-reported emission estimates with the aircraft flight studies implying a significantly higher level of CO2 emissions in the region of 17 megatonnes (MT) per year. We suggest that these apparent discrepancies can be explained by the uncertainty and bias associated with the methods and procedures used in the ref. 1 analysis. It is essential that these discrepancies be verified as there are potentially significant financial implications from these emission discrepencies—$1.105 billion per year at a rate of $65/tonne.