The present invention provides the use of from 0.1 to 5 wt%, based on overall gasoline composition, of a base oil having a kinematic viscosity at 100 °C of at least 1 cSt, in a gasoline composition comprising a major amount of gasoline, for improving the acceleration response of a four-stroke spark-ignition internal combustion engine fuelled by the gasoline composition. The present invention further provides a method of operating a four-stroke spark-ignition internal combustion engine, which method involves introducing into a combustion chamber of said engine a gasoline composition comprising: (a) a major amount of a gasoline; and (b) from 0.1 wt% to 5 wt%, based on the overall gasoline composition, of a base oil having a kinematic viscosity at 100 °C of at least 1 cSt.