Assessment of the risk of oil spills impact on the environment is necessary as a starting condition for the development of a set of measures to ensure environmental safety in water areas where exploration, production and transportation of oil and oil products are carried out or planned. The nomenclature and form of presentation of data used in drawing up oil spill response plans are considered. An accidental oil spill at sea is presented as a random event, the time, place and scale of which are difficult to predict. The assumption is made that all information about the emergency, except the time of the emergency, is known, and the basic principles of risk assessment are given. To demonstrate the output of the risk-analysis of oil spill spreading the reconstruction of hydrometeorological conditions for the water area of the Gulf of Ob in the Kara Sea is carried out and the results of typical calculations for a conditional point of diesel fuel discharge are given.