In the paper, qualitative indicators, the changes in rheological properties of different types of oils and their mixtures have been investigated on the base of laboratory tests. Depending on the type and mass fraction of mixed products, additive changes in the properties for most mixtures, the existence of positive and negative synergism in them have been discovered. In order to prevent the complications associated with the mixing of oils, initially, the necessity of their extensive investigation in laboratory conditions has been shown. One of the main reasons of anomaly that occurs is the chemical composition of the mixed oils (asphalt,paraffin and amount of resin compounds).