A shape of marine slicks is an important characteristic which can be used when solving a problem of detection and identification of oil spills on the sea surface. Slick shape and its spatial-temporal evolution depend on many environmental processes, such as wind speed, nonuniform marine currents, internal waves, etc. In the context of the problem of oil spill dynamics it is very important, particularly at initial stages of oil spill evolution, to describe correctly processes of oil film spreading. Until recently the most popular was the Fay’s model of film spreading which, however, could not correctly explain some obvious effects, e.g., asymmetry of film slicks in the downwind and crosswind directions. In this paper new results of field studies of spreading of surfactant films are presented. The experiments with spills of surfactants were conducted on the Gorky water reservoir using a methodology of contouring slicks with a GPS receiver mounted on a motor boat, and also aerial photography from UAV. The following results have been obtained. First, the effect of elongation of oil spills in the wind direction, revealed in our previous experiment, is confirmed. Quantitative data on growth rates of along- and cross-wind slick axes are obtained characterizing initial stages of the spreading process. Second, new effects have been revealed which are: a) saturation of the cross- and along-wind axes at some intermediate stages of slick evolution, and b) further decrease of the along wind slick axis and the slick square, and a tendency to a circular shape at late stages of the slick evolution. A physical model, explaining qualitatively the observed effects is developed.