burn the midnight oil

Originally referring to the act of burning lamp oil in oil lamps for light at night. The collocation midnight oil in its literal sense is attested from mid 17th c.

• "Near-synonym: pull an all-nighter"
• "He was burning the midnight oil to finish his paper."
• "She was burning the midnight oil to finish her part of the project."
• "You worked at whatever task you were engaged in — churning out steel nuts for the car companies or churning out essays in college — until you were done, even if you had to burn the midnight oil. No excuses, no whining, no cheating."

• elucubrate
• pull an all-nighter

• burn the candle at both ends
• candlewasting