Oil prices extended their decline due to higher US crude stockpiles, signaling oversupply concerns in the market.Brent traded below $65 a barrel and West Texas Intermediate near $61, with commercial inventories of crude rising for a second week.Worries about an oversupplied market, wider financial market retreats, and concerns about Washington's deficit contributed to the decline.OPEC and its allies pushing more barrels into the market, US-led trade war worries about global economic growth slowing also impacted prices.