Oil prices fell on Thursday, under pressure from rising supplies both in the United States, where inventories gained for a sixth straight week, and in Europe, where physical crude prices are nearing five-month lows.
On Wednesday, oil dropped nearly 4 percent after the Energy Information Administration said U.S. crude inventories added 2.85 million barrels last week, in line with forecasts, despite a fall in imports to their lowest level since 1991.
Prices briefly came off their session lows in midday trade as the erased most early losses, but crude futures were testing those lows once again as U.S. crude headed into the day's settlement.
U.S. WTI crude closed down $1.12, or 2.42 percent, at $45.20 a barrel after declining 3 percent in the previous session.
futures were down 70 cents at $48 a barrel, some 4 percent below four-week highs above $50 hit two days earlier.
Oil contracts were also tracking weak gasoline prices. Gasoline futures lost nearly 1 percent, extending Wednesday's 4-percent tumble, amid worries of peak turnout from U.S. refineries as the autumn maintenance cycle draws to a close.
"What we're seeing is not a good sign for November," said Scott Shelton, oil broker and commodities specialist at ICAP in Durham, North Carolina.
Market intelligence firm Genscape added to the bearish sentiment in crude oil, estimating a build of over 383,000 barrels at the Cushing, Oklahoma delivery point for U.S. crude futures in the week to Nov. 3, traders who saw the data said.
According to Genscape, Cushing took in nearly 713,000 barrels in the four days to Nov. 3, showing a supply onslaught late in that week which most likely offset an earlier draw, the traders said.
Outside of the United States, supply of North Sea crude, which underpins Brent prices, is also ample, pushing the global crude benchmark to June lows.
Brent's spot contract and oil slated for delivery in a year was at a discount, or "contango", of nearly $7 a barrel, the biggest in two months.
"The difficulty right now for the market is being able to lift off from the current floor that it has found in the mid-$40s on a WTI basis," said BNP Paribas global head of commodity strategy Harry Tchilinguirian said.
"For that to happen, the market needs to see, at least directionally, some form of improvement, whether that translates into significantly lower production in the U.S. or at least much stronger refinery runs."
—CNBC's Tom DiChristopher contributed to this story.