The ignition of a liquid fuel under high intensity radiation was studied experimentally to obtain a fundamental understanding of the ignition mechanism and to aid in the selection of design improvements to minimize hazards of unwanted fires. The experiments were conducted using a CW CO2laser with incident fluxes from 1000 to 5000 W/cm2andn-decane as the flammable liquid. The study of the effect of the container size showed 6 cm diameter by 5 cm depth sufficiently large to prevent container size effects on ignition. High speed photographs of ignition events showed the motion of decane prior to ignition and the onset of the ignition in the gas phase. The effect on ignition of the incident angle of the laser beam with respect to the decane surface was studied from 90° to 30°. On reducing the incident angle, the ignition delay time becomes longer and the minimum incident flux for ignition increases significantly. The proposed autoignition mechanism of decane by a CO2laser is the absorption of the incident laser beam energy by the vapor plume.