The paper is focused on particularities of offshore oil-and-gas fields’ construction and commercial operation that are taken into account within the economic-mathematical modeling, and the configuration of the production – transport system’s structural components. Description of principal blocks comprising the model, and the list of calculated economic and investment parameters are given. The general view of the block «Calculation of financial flows and basic economic and investment parameters» is presented. The model was tested in a number of works performed by the Institute on substantiation of investments into offshore oil and gas fields construction and production.