Lubricating Oil Composition for Internal-combustion Engine, and Method for Reducing Friction in Gasoline Engine

Provided is a lubricating oil composition for internal combustion engines capable of exhibit a sufficient friction-reducing effect from a low-temperature range assuming engine starting to a practical temperature range of 80° C. or higher. The lubricating oil composition for internal combustion engines contains a surfactant having an alkylene oxide as the constituent unit and having an HLB value of 7 or more and less than 15, and a lubricant base oil.