The present work is devoted to the description of current state of the collective transport theory in liquids. In this connection, the results of MD-modelling of the root mean square displacement and the velocity autocorrelation function of a molecule (VACFM) at sufficiently large times are discussed. The characteristic function allowing to estimate the relative value of collective contributions to self-diffusion coefficient is introduced and studied in details. The low-frequency spectra of the VACFM are used for the determination of the Maxwell relaxation time, playing the key role in approach presented. The possibility of determination of binodal and spinodal positions by the temperature dependences of self-diffusion coefficients on isochores, is considered.