Traditional solar-energy collection systems experience high thermal losses because of the high surface temperature of the absorber. Nanofluid developments have led to extensive studies on their suitability for direct absorption as solar-energy collectors. A potential approach for solar steam generation via nanoparticle absorption of solar light and its conversion to thermal energy for water evaporation has been introduced recently. Direct solar vapor generation enabled by carbon-nanotube nanofluids was investigated experimentally in the present work. The effects of solar-power density and carbonnanotube concentration on solar steam-generation performance are discussed. The evaporation rate increases with an increase in solar power and carbon-nanotube concentration. A high evaporation efficiency (46.8%) was obtained with a 19.04 x 10(-4) vol.% carbon-nanotube nanofluid under a solar illumination power of 10 Sun (1 Sun =1 kW m(-2)). A high evaporation rate was achieved by localized heating of the nanofluid rather than by a bulk temperature increase, which provides a mechanism for low temperature solar vapor generation and exhibits broad solar-energy applications such as seawater desalination, waste sterilization and power generation. (C) 2016 Elsevier Ltd. All rights reserved.