Co-feeding experiments have shown that ethers can participate substantially in the Fischer-Tropsch synthesis with iron catalysts. Dimethyl ether is thought to be capable of building up surface complexes which are very similar to those naturally occurring during synthesis. Diethyl ether undergoes rapid reaction, probably deoxygenation to ethene, which in turn initiates hydrocarbon synthesis. The results show that important similarities exist in the nature of the hydrocarbon synthesis in the Fischer-Tropsch and methanol-to-gasoline processes. While ethers are similar to naturally occurring synthesis intermediates, aldehydes are quite different and their presence suppresses and entirely changes normal synthesis behaviour. The results underline the important role that oxygenates can play in hydrocarbon synthesis on iron catalysts. When alkenes are co-fed, the olefin selectivity increases in the order of constant concentrations of ethene < propene < butene, until a maximum value is reached of about 95%. The reactivity towards hydrogen was found to be propene < butene < ethene.