Lubricating oil composition and method for reducing friction in internal combustion engines

A lubricating oil composition, comprising:

• (A) a lubricating base oil comprising mineral oil;
• (B) a molybdenum-based compound comprising a binuclear organic molybdenum compound of formula (I):
• wherein
• R1 to R4 each represents a hydrocarbon group having 4 to 22 carbon atoms,
• and R1 to R4 may be the same as or different from each other, and
• X1 to X4 each represents a sulfur atom or an oxygen atom;
• (C) a metal-based detergent comprising (C1) a calcium detergent comprising a calcium salicylate and (C2) a magnesium detergent;
• and
• (D) an ester compound of formula (III):
• wherein:
• R10 is a hydrocarbon group having from 12 to 24 carbon atoms;
• and
• R11 to R15 are each a hydrogen atom,
• wherein a content of the lubricating base oil (A) is 75 mass % or more and 97 mass % or less based on a total amount of the lubricating oil composition,
• wherein a content of the molybdenum compound (B) as converted into a molybdenum atom is 0.03 mass % or more and 0.12 mass % or less on a basis of the total amount of the lubricating oil composition,
• wherein a content of the calcium detergent (C1) as converted into a calcium atom is 0.1 mass % or more and 0.20 mass % or less on a basis of the total amount of the lubricating oil composition,
• wherein a content of the magnesium detergent (C2) as converted into a magnesium atom is 0.02 mass % or more and 0.10 mass % or less on a basis of the total amount of the lubricating oil composition, and
• wherein a content of the ester compound (D) having one or more hydroxyl groups in a molecule thereof is 0.05 to 1.00 mass % on a basis of the total amount of the lubricating oil composition.