We have demonstrated large-scale production (10 g/day) of high-purity carbon single-walled nanotubes (SWNTs) using a gas-phase chemical-vapor-deposition process we call the HiPco process. SWNTs grow in high-pressure (30-50 atm), high-temperature (900-1100 degreesC) flowing CO on catalytic clusters of iron. The clusters are formed in situ: Fe is added to the gas flow in the form of Fe(CO)(5). Upon heating, the Fe(CO)(5) decomposes and the iron atoms condense into clusters. These clusters serve as catalytic particles upon which SWNT nucleate and grow (in the gas phase) via CO disproportionation: CO + CO==>CO2 + C(SWNT). SWNT material of up to 97 mol % purity has been produced at rates of up to 450 mg/h. The HiPco process has been studied and optimized with respect to a number of process parameters including temperature, pressure, and catalyst concentration. The behavior of the SWNT yield with respect to various parameters sheds light on the processes that currently limit SWNT production, and suggests ways that the production rate can be increased still further.