> However my gut feeling is that Oil&Gas refinery and extraction are grossly under reporting Methane emissions. So it could be that the chart doesn't show the full picture of GHG.

There's been a fair amount of focus on this in the past ~5 years. We can constrain methane emissions both from a "bottoms-up" (measuring direct-from-source emissions or tallying up expected emissions given natural gas production and leakage rates) and "top-down" (measuring atmospheric CH4 over time and constraining the year-to-year emissions required to drive observed changes). Work like Rutherford et al (2021; https://www.nature.com/articles/s41467-021-25017-4) definitely leave room for some unaccounted leakages arising from O&NG production, but there likely is not room for much more "grossly under reported" emissions.