"Production restarted on Sunday, although it's still not back to full capacity," said a Repsol spokesman.
Libya's 340,000 barrels-per-day El Sharara oil field, owned and operated by Repsol, located in the remote south of the country, has been repeatedly closed by armed groups and protestors as a way to pressure Libya's weak central government into political and financial demands.
Disruption in Libya contributed to Repsol posting a loss last month in its results for the past year. The country accounts for around 12 per cent of Repsol's total output.
Analysts estimate the shutdown of the oil field cost Repsol some 30 million euros, or 1 million euros per day in net profit.
Three years of turmoil since the overthrow of Muammar Gaddafi and tough contract terms have prompted some oil companies to reassess their positions in Libya and several have said they would postpone projects or scrap them altogether.