• Brent crude fell to roughly $56-per-barrel, while WTI, the U.S. benchmark, dropped sharply into the $46-per-barrel range.
• But they're more or less holding steady on Wednesday morning, trading around $56.58 for Brent and $46.85 for WTI.

Why it matters: The falling prices create challenges for petro-states and could hinder the U.S. shale patch if the doldrums remain.

• Here's Bloomberg: "The plunge in U.S. oil prices has wells in some parts of the Permian Basin below break-even levels, threatening to put the brakes on the record flow from the prolific field."

The big picture: Concerns about a slowdown in economic growth and trade battles eating into demand, the robust amount of crude sloshing around, and broader market woes are all creating downward pressure on prices.

• Brent has come down from $86 in early October, its highest level in 4 years, while WTI has come down by around $29 since then.

What they're saying: “The market is experiencing price carnage, maximum pain and considerable downside pressure,” Robin Bieber of the brokerage PVM oil tells Reuters.

• "Enveloping supply concerns is the increasing likelihood of a protracted economic downturn in China that continues to stoke fears of demand slowdown," Stephen Innes of the trading platform Oanda said in a note quoted by MarketWatch.

What's next: Late this morning the Energy Information Administration will release its closely watched weekly data on U.S. oil storage levels.

Go deeper: Oil prices volatile after OPEC-Russia deal