The paper presents preliminary data on the application of dynamical current-voltage characteristics (DCVC) approach to diagnostics of dielectric liquid aging. Several samples of oils used in power transformers were investigated. The data were measured in a blade-plane cell at the negative polarity in the range from 0 to 25 kV using the voltage saw-tooth modulation. The DCVCs were shown to be sensitive to the operating time of oil and degassing treatment. Some kind of high-voltage conductivity 'activation' and 'deactivation' processes were revealed, which calls for further investigation.