Low transition temperature mixtures (LTTMs) comprising a eutectic mixture of a quaternary amine and a polyol such as glycol are provided. The LTTMs can provide various beneficial properties, such as highly desirable viscosity index, low glass transition temperatures, and/or high kinematic viscosities relative to the molecular weight of the mixture components. The mixtures can be advantageously used as co-base stocks in lubricating oil compositions.