Why Oil Prices Slumped to 2013 Low

Andrey Rudakov | Bloomberg | Getty Images

An employee walks past a conveyor belt at a Royal Dutch Shell processing plant.

U.S. oil prices closed at the lowest level of 2013, after falling below $92 a barrel intraday Tuesday.

Brent crude is down nearly $2, trading below $113 a barrel, poised for the lowest settlement price since Jan. 29.

(Read More: US Manufacturing to Take Off on Cheap Energy: Pickens)

Here's what traders say is contributing to the selloff:

• Italy's election stalemate has escalated worries over the eurozone debt crisis and fuel demand
• Iran's talks with Western nations over its nuclear program have reduced the geopolitical risk premium in the oil markets
• Refineries resuming operations after planned maintenance or shutdowns has caused a big slide in refined fuels, dragging down overall oil market.

Gasoline futures are down 2.5 percent, also at their lowest levels in a month. Prices were pressured after Motiva Enterprises announced earlier Tuesday it is restarting operations at its gasoline-making unit in Port Arthur, TX. Motiva is joint venture between Royal Dutch Shell and Saudi Aramco.

(Read More: Pro: Why It's Time to Get Into Nat Gas)

—By CNBC's Sharon Epperson; Follow her on Twitter: @sharon_epperson

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