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