Oil prices declined on the Fed's interest rate decision. The Fed kept its interest rate unchanged at 0.00%-0.25%.

The Fed took into account the slowdown in the global economy and low inflation expectations. That was the main reason to keep the monetary policy unchanged.

"Recent global economic and financial developments may restrain economic activity somewhat and are likely to put further downward pressure on inflation in the near term," the Fed said.

The Fed's decision led to a weaker U.S. dollar. Oil prices are traded in U.S. dollars. A weaker U.S. dollar leads to higher demand in oil and to higher oil prices. But oil prices today declined despite this fact.

Russian Deputy Energy Minister Alexei Teksler said on Friday that Russia will cut its oil output if the oil price declines below $40 a barrel.

"If the price falls below $40 per barrel, then we, most likely, would be faced with a production decline," he said.

Teksler noted that oil companies have to adjust their models if oil is persistently below $45 a barrel.

"With a price of $40-$45 per barrel, the companies will revise their models, if the low price persists long term. Previously approved models would stop working efficiently," he said.

Market participants are awaiting the release of the number of active U.S. rigs later in the day. The oil driller Baker Hughes reported that the number of active U.S. rigs declined by 10 rigs to 652 last week.

WTI crude oil for October delivery declined to $45.06 a barrel on the New York Mercantile Exchange.

Brent crude oil for October decreased to $48.00 a barrel on ICE Futures Europe.