Carbon-carbon bond formation pathways during CO hydrogenation to higher alcohols were studied on alkali-promoted Cu-based catalysts (K-CuMgCeOx and Cs-Cu/ZnO/Al2O3) using (CO)-C-13/H-2/(CH3OH)-C-12 reactants. C-C bonds in ethanol form via two pathways, direct reactions of (CO)-C-13 and direct coupling of (CH3OH)-C-12. On K-Cu0.5Mg5CeOx, direct reactions of (CO)-C-13 are the predominant pathway for the initial C-C bond steps. On Cs-Cu/ZnO/Al2O3, ethanol is predominantly formed via direct coupling of oxygen-containing C-1 intermediates derived from (CH3OH)-C-12. Cs+ cations introduce a methanol-coupling pathway unavailable on catalysts without Cs+ promoter, leading to higher alcohol synthesis rates. After ethanol formation, additional chain growth occurs via aldol-type coupling pathways using C1 intermediates derived from (CH3OH)-C-12 on both K-Cu0.5Mg5CeOx and Cs-Cu/ZnO/Al2O3 catalysts.