Just found this summary of an engineering symposium by @exxonmobil from 1981. More than a fourth of their effort (in the wake of the 1970s energy crises) was on synfuels, which they estimated would require 20-25 years for maturity. Other work was on oil shale.

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Great thread here. With a helpful dose of humility for all of us trying to build or predict the future of energy.