A ministry statement, published on state media, did not name the firm involved in the deal with the Syrian Democratic Forces (SDF), an alliance that seized swathes of north and east Syria from Islamic State with US help.
According to Reuters the statement did not give details on the agreement.
There was no immediate response from SDF officials to a Reuters’ request for comment and there was no immediate comment from US officials.
Damascus “condemns in the strongest terms the agreement signed between al-Qasd militia (SDF) and an American oil company to steal Syria’s oil under the sponsorship and support of the American administration”, the statement said.
“This agreement is null and void and has no legal basis,” it said, adding that it was a violation of Syrian sovereignty.
Syria produced around 380,000 barrels of oil per day before a civil war erupted, with Iran and Russia backing President Bashar al-Assad’s government and the United States supporting the opposition.
Damascus lost control of most oil producing fields in a stretch east of the Euphrates River in Deir al-Zor. Western sanctions have also hit the energy industry.
US President Donald Trump has said that despite a military pullback from northeast Syria, a small number of American forces would remain “where they have oil”. The Pentagon said late last year that oilfield revenues would go to the SDF.
Reporter's code: 50101