The present invention aims to provide a viscosity index improver excellent in shear stability and having a low HTHS viscosity and a high viscosity index. The viscosity index improver of the present invention contains a (co)polymer (A) containing a polyolefin-based monomer as an essential monomer unit, and a base oil, wherein the absolute value of difference in solubility parameter between the (co)polymer (A) and the base oil is 0.8 to 2.0 (cal/cm.sup.3).sup.1/2.

This disclosure describes a lubricating oil composition that includes a major amount of an oil of lubricating viscosity and one or more nitrogen-containing additive having the formula:

##STR00001##

wherein R.sup.1 is functional group containing 10 to 250 carbon atoms; and R.sup.2 and R.sup.3 are independently functional groups containing 2 to 20 carbon atoms.

This disclosure describes a lubricating oil composition that includes a major amount of an oil of lubricating viscosity and one or more nitrogen-containing additive having the formula:

##STR00001##

wherein R.sup.1 is functional group containing 10 to 250 carbon atoms; and R.sup.2 and R.sup.3 are independently functional groups containing 2 to 20 carbon atoms.

The present invention aims to provide a viscosity index improver excellent in shear stability and having a low HTHS viscosity and a high viscosity index. The viscosity index improver of the present invention contains a (co)polymer (A) containing a polyolefin-based monomer as an essential monomer unit, and a base oil, wherein the absolute value of difference in solubility parameter between the (co)polymer (A) and the base oil is 0.8 to 2.0 (cal/cm.sup.3).sup.1/2.

The present invention aims to provide a viscosity index improver excellent in shear stability and having a low HTHS viscosity and a high viscosity index. The viscosity index improver of the present invention contains a (co)polymer (A) containing a polyolefin-based monomer as an essential monomer unit, and a base oil, wherein the absolute value of difference in solubility parameter between the (co)polymer (A) and the base oil is 0.8 to 2.0 (cal/cm.sup.3).sup.1/2.

This disclosure describes a lubricating oil composition that includes a major amount of an oil of lubricating viscosity and one or more nitrogen-containing additive having the formula: ##STR00001##
wherein R.sup.1 is functional group containing 10 to 250 carbon atoms; and R.sup.2 and R.sup.3 are independently functional groups containing 2 to 20 carbon atoms.

This disclosure describes a lubricating oil composition that includes a major amount of an oil of lubricating viscosity and one or more nitrogen-containing additive having the formula: ##STR00001##
wherein R.sup.1 is functional group containing 10 to 250 carbon atoms; and R.sup.2 and R.sup.3 are independently functional groups containing 2 to 20 carbon atoms.