It is proposed that the complex electrical conductivity of an ideal fluid liquid mixture is expressed as the sum of pure-component complex electrical conductivities weighted by their volume fractions in the mixture. The relevance of the corresponding excess property in the investigation of enhanced electrical conductivity of nanofluids is highlighted for the case where the base fluid consists of ethylene glycol–water mixtures. New measurements of the direct current conductivity were made for these mixtures at 298.15 K. It is pointed out that different published experimental measurements lead to excess electrical conductivity values with opposite signal. These discrepancies are discussed and possible explanations advanced. The proposed analysis of electrical conductivity is adapted to binary systems of nanofluidbase fluid and, using literature data, the usefulness of excess electrical conductivity is demonstrated. Financiado para publicación en acceso aberto: Universidade de Vigo/CISUG Xunta de Galicia | Ref. ED431C 2020-06 Fundação para a Ciência e a Tecnologia | Ref. UIDB/00100/2020