Oil prices declined on concerns over the slowdown in the Chinese economy and concerns over the global oil slowdown. Market participants expect the oil supply to rise when sanctions against Iran will be lifted off.

Market participants are awaiting the release of the Chinese preliminary manufacturing purchasing managers' index (PMI) tomorrow. The index is expected to rise to 47.5 in September from 47.3 in August.

Meanwhile, the Asian Development Bank (ADB) lowered growth forecasts for China. According to the ADB, China is expected to expand by 6.8% in 2015, down from July estimate of a 7.0% rise, and 6.7% in 2016, down from July estimate of a 6.8% increase.

Market participants are awaiting the release of U.S. crude oil inventories data. The American Petroleum Institute (API) is scheduled to release its U.S. oil inventories data later in the day, and U.S. oil inventories data from the U.S. Energy Information Administration is expected on Wednesday.

WTI crude oil for October delivery fell to $45.46 a barrel on the New York Mercantile Exchange.

Brent crude oil for October declined to $47.96 a barrel on ICE Futures Europe.