We have demonstrated scalable and selective synthesis of carbon nanotubes (CNTs), carbon nanofibers (CNFs), and onion-like carbon (OLC) in a batch reactor using supercritical fluids (SCF) as reaction media. The process utilizes toluene and alcohols (ethanol, propanol, and butanol) as carbon precursors in combination with ferrocene. Growth with supercritical toluene at 600ºC in the absence of water yield large-diameter CNTs and CNFs while the introduction of 2.78 mmol/L of water enhances the product yield by 50% and promotes the formation of smaller-diameter CNTs and the exterior surface of CNTs was decorated with Fe nanoparticles. At 400ºC, in the absence of water, supercritical toluene produces mainly OLCs and the selectivity increases with introduction of water, peaking at 5.55 mol/L. For alcohols, there is a gradual evolution of the morphology of nanocarbons formed from mainly OLCs as the ratio of C/O atoms increases to tube like structures, possibly due to a decrease in the tendency of graphitic sheets to minimize their energies by curling into onion-like structures as chain length increases. This study provides a framework for utilizing SCF reaction media in a batch reactor to achieve scalable and selective growth of different nanocarbons and nanocarbon-metal nanocomposites.