CO is an abundant, cheap source of carbon and oxygen atoms. It can be readily obtained from fossil fuel sources including coal and natural gas. Many renewable sources of CO gas are also available: biomass, wood waste, and recycled plastics. Further, CO can be produced from CO2 directly by the water-gas shift reaction (Eq. 1). Key industrial processes use CO as a building block. For example, the Cativa process produces acetic acid by the iridium catalysed carbonylation of methanol at the 500,000-ton scale annually. Similarly, the hydroformylation 'oxo' process produces aldehydes from alkenes through the net addition of a formyl (CHO) unit to saturated carbon-carbon bonds. The Fischer-Tropsch (FT) process provides liquid hydrocarbons from syn-gas, mixtures of CO and H 2 , and can be considered as the controlled hydrogenation and homologation of CO. The FT process consumes tens of thousands of barrels of crude oil daily to produce petroleum fuel. Under certain geopolitical conditions, the cost of fuel production through the FT process is economically competitive with the crude oil fossil-fuel source. Examples include Qatar and South Africa, where Pearl GTL and SASOL factories produce liquid hydrocarbons and lubricants industrially.