Disclosed is a method of reducing the rate of depletion of basicity (as determined by ASTM D2896) of a lubricating oil composition in use in an engine. The lubricating oil composition includes at least one overbased alkali or alkaline earth metal detergent. The method comprises adding to the lubricating oil composition one or more compounds of Formula (I): (see formula I) wherein: x is 1 to 50, preferably 1 to 40, more preferably 1 to 30; R1 and R2 are H, hydrocarbyl groups having 1 to 12 carbon atoms, or hydrocarbyl groups having 1 to 12 carbon atoms and at least one heteroatom; R is a hydrocarbyl group having 9 to 100, preferably 9 to 70, most preferably, 9 to 50, carbon atoms; and n is 0 to 10, or alkaline earth metal salts thereof. The compounds of formula (I) are preferably methylene-bridged alkyl phenols or ethoxylated methylene-bridged alkyl phenols.