Catalytic chemical vapor deposition (CVD) utilizing the gaseous product mixture of Fischer-Tropsch synthesis (FTS-GP) offers the potential for scale-up and controlled growth of carbon nanotube (CNT) carpets. In comparison to conventional feedstocks, FTS-GP exhibits the ability to support an exceptionally long catalyst lifetime with Fe catalysts. The role of the feedstock in growth enhancement is still poorly understood. In this study, a combination of experimental and thermodynamic analyses reveal on-site generation of water to be the secret for observed growth enhancement in FTS-GP CVD. The concentration of water generated in situ decreases with increasing reactor temperature. Further investigations using an Autonomous Research System (ARES)-an automated, high-throughput, laser-induced CVD system with in situ Raman spectral feedback-reveal FTS-GP not only exhibits exceptionally long catalyst lifetimes compared to a standard feedstock (C2H4), but also shows a high tolerance for relatively high levels of water.