burn the midnight oil, to

To stay up late working on a project or task. The phrase refers to the outdated practice of using an oil lamp. Denise has been burning the midnight oil trying to finish this report, so she must be exhausted. I'll need to burn the midnight oil to have any chance of finishing this paper before class tomorrow morning.

Fig. to stay up working, especially studying, late at night. (Alludes to working by the light of an oil lamp late in the night.) I have a big exam tomorrow so I'll be burning the midnight oil tonight. If you burn the midnight oil night after night, you'll probably become ill.

Stay up late working or studying, as in The semester is almost over and we're all burning the midnight oil before exams. This expression alludes to the oil in oil lamps. [Early 1600s]

If you burn the midnight oil, you stay up very late at night in order to finish a piece of work. He's been burning the midnight oil getting his article written. The truth is, I haven't been sleeping all that much lately. Burning the midnight oil. Note: The image here is of someone working late into the night by the light of an oil lamp.

To work or study very late at night.

To stay up late, studying or working. This expression, which may well be as old as the first oil lamp, appeared in English in the mid-seventeenth century. It has been traced to a poem by Francis Quarles (“Emblems,” 1635): “Wee spend our midday sweat, or midnight oyle; wee tyre the night in thought; the day in toyle.” A more recent example is found in David Baldacci’s Hour Game (2004): “You don’t want to burn the midnight oil too much; it’s bad for your complexion.”