The timetable for disarmament was laid down by U.S. Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov a week ago in Geneva when they set aside sharp differences over Syria to address the chemical weapons issue.
Their plan set a Saturday deadline for Syria to give a full account of the weapons it possesses. Security experts say it has about 1,000 tonnes of mustard gas, VX and sarin - the nerve gas U.N. inspectors found had been used in the Aug. 21 attack.
The U.S. State Department said on Friday, after the OPCW announced Syria's initial declaration, that it was studying the material. "An accurate list is vital to ensure the effective implementation," spokeswoman Marie Harf said.
Once the OPCW executive has voted to follow the Lavrov-Kerry plan in a meeting expected early next week, the Security Council is due to give its endorsement of the arrangements - marking a rare consensus after two years of East-West deadlock over Syria.
However, the two powers are divided over how to ensure compliance with the accord. U.S. President Barack Obama has warned that he is still prepared to attack Syria, even without a U.N. mandate, if Assad reneges on the deal.
Russia, which says it is not clear who was behind the Aug. 21 attack and has a veto in the Security Council, opposes attempts by Western powers to write in an explicit and immediate threat of penalties under what are known as Chapter VII powers.