Use of a lubricating oil comprising: (a) a base oil comprising a bimodal blend of two different base oils, i. a first base oil being one or more oils selected from the group consisting of Group III base oils, Group IV base oils and Group V base oils, which first base oil has a kinematic viscosity at 100°C of from 2 to 12 mm 2 /s, and ii. a second base oil being one or more oils selected from Group IV base oils having a kinematic viscosity at 100°C of at least 38 mm 2 /s, the difference in kinematic viscosity between the first and second base oils in the blend being at least 32 mm 2 /s, and the combination of the first and second base oils having a kinematic viscosity at 100°C of 15 mm 2 /s or less, (b) a detergent selected from an alkali and/or alkaline earth metal salicylate or a mixture of alkali and/or alkaline earth metal phenates and alkali and/or alkaline earth metal salicylates, the detergent being present in a total amount of 0.5 to 6 wt% of the lubricant (based on detergent active ingredients), as an engine oil for lubricating large low and medium speed engines in which the velocity at which interfacing surfaces of the engine move past each other when the engine is operating reach at least 3 mm/s for improving the fuel economy of said engines, wherein said interfacing surfaces are selected from the group consisting of piston and cylinder wall and/or interfacing bearing surfaces, wherein the improvement in fuel economy is evidenced by the engine oil having a traction coefficient which is lower than the traction coefficient of engine oils which are not bimodal or which are not bimodal to the same degree as recited or which are based on Group I and/or Group II base oils, and which do not contain the aforesaid detergents, and wherein the traction coefficient is measured using an automated mini traction machine measurement instrument (MTM traction rig) at a temperature of 100°C, under a load of 1.0 GPa, a slide-to-roll ratio of 50% and a speed gradient of 0-3000 mm/s in 480 seconds. (a) a base oil comprising a bimodal blend of two different base oils, i. a first base oil being one or more oils selected from the group consisting of Group III base oils, Group IV base oils and Group V base oils, which first base oil has a kinematic viscosity at 100°C of from 2 to 12 mm 2 /s, and ii. a second base oil being one or more oils selected from Group IV base oils having a kinematic viscosity at 100°C of at least 38 mm 2 /s, the difference in kinematic viscosity between the first and second base oils in the blend being at least 32 mm 2 /s, and the combination of the first and second base oils having a kinematic viscosity at 100°C of 15 mm 2 /s or less, i. a first base oil being one or more oils selected from the group consisting of Group III base oils, Group IV base oils and Group V base oils, which first base oil has a kinematic viscosity at 100°C of from 2 to 12 mm 2 /s, and ii. a second base oil being one or more oils selected from Group IV base oils having a kinematic viscosity at 100°C of at least 38 mm 2 /s, (b) a detergent selected from an alkali and/or alkaline earth metal salicylate or a mixture of alkali and/or alkaline earth metal phenates and alkali and/or alkaline earth metal salicylates, the detergent being present in a total amount of 0.5 to 6 wt% of the lubricant (based on detergent active ingredients),