The term 'controlled production' of single-wall nanotubes (SWNT) implies the ability to control the selectivity towards SWNT by changing catalyst formulations and operating conditions, combined with a quantitative measurement of the SWNT obtained. In this contribution, a significant advancement towards the controlled production of SWNT is reported. A family of Go-Mo catalysts has been found to be able to produce SWNT with high selectivity, depending on the Co:Mo ratio, the temperature of operation, and the processing time. The optimization of the catalyst was possible by the application of a simple and direct method of quantification of the SWNT production.