The optimumcatalyst formulation identified through this study showed a25% improvement in C2–C4selectivity compared to Sasol’s bestin-house prepared precipitated iron catalyst. The methodology fol-lowed in this study, namely to plot the grouped C2–C4selectivityas a function of the methane selectivity together with the idealSchulz Flory correlation, is a simple but quite effective evaluationcriteria for the novel Na–S promoted FTS catalysts. If a significant“excess” amount of C2–C4components is produced the result willbe a high overall selectivity to light chemicals (olefins and alco-hols). However, it was shown in this work that the propensity of thisnovel group of catalysts to yield a product slate that deviates fromthe Schulz Flory correlation is significantly reduced at high catalystactivity and CO conversion levels. From the results it is clear thatsulphur in combination with alkali (sodium or potassium) leads toa selectivity shift towards C2–C4hydrocarbon fraction without anincrease in methane selectivity.