The United Nation's Human Rights Council says more than 60,000 people have been killed since the start of the Syrian uprising in March 2011.
The Benetech research group looked at 147,349 reports of deaths from seven sources.
Duplicate names were removed and only accounts that provided the first and last name of the victim, and the date and location of death, were counted. After this process, a figure of 59,648 was reached.
However, UN human rights commissioner Navi Pillay said the figure would now be above 60,000.
The study did not provide a breakdown of whether those who died were rebels, soldiers or civilians. But 76% were identified as male.
The worst areas were rural Damascus and Homs province.
The BBC reports the researchers also said an unknown number of killings had not been documented by any of their sources.
Dozens of people have been killed by an air strike on a petrol station in the outskirts of the Syrian capital, Damascus.
Residents said they saw burning bodies and horrific scenes after the air strike.
Unverified reports said up to 70 people had been killed.
The BBC reports that rebels now control large sections of Syria, but the conflict has appeared to be largely stalemated for months.