"Regime forces and allied gunmen retook control of parts of the Jazal oilfield in the Homs countryside which IS had captured 48 hours earlier," said the Syrian Observatory for Human Rights.
The Britain-based monitor said, however, that IS militants were still in control of a housing complex for oil workers in the town of Jazal and said that clashes were underway nearby.
Jazal is the last major oilfield under the control of the Syrian government.
Oil production has since been halted at Jazal, which previously produced 2,500 barrels of oil per day.
The oilfield has changed hands before, with IS briefly capturing it in June before regime forces retook it.