Stochastic models are often economical to generate but problematic to render. Most previous algorithms first generate a realization of the stochastic model and then render it. These algorithms become expensive when the realization of the stochastic model is complex, because a large number of primitives have to be rendered. In stochastic rendering we also model the intensity as a random field, and the statistics of the intensity field are related to the statistics of the stochastic model through an illumination model. Stochastic rendering algorithms then generate a realization of the intensity field directly from the statistics. In other words, a random component is shifted from the modelling to the rendering. This paradigm is not entirely new in computer graphics, so related work will be discussed. The main contribution of this paper is a stochastic rendering algorithm of gaseous phenomena modelled as random density fields such as clouds, smoke and fire. A simplified version of the scattering equation is used to derive the statistics of the illumination field. Our algorithm is therefore an improvement over similar algorithms both in terms of computational speed and generality.