NEW YORK (TheStreet) -- Marathon Petroleum Corp. (MPC - Get Report) stock is plunging 7.50% to $32.32 in afternoon trading on Friday as overproduction continues to push oil prices down, despite a decline in the U.S. rig count.

WTI crude is falling 2.74% to $30.85 per barrel on the New York Mercantile Exchange, while Brent crude is declining 1.25% to $34.03 per barrel on the Intercontinental Exchange this afternoon.

The number of active rigs dropped for the seventh week in a row this week. U.S. energy companies took 31 rigs out of production, bringing the total count to 467, according to Baker Hughes (BHI) data. 

"Volatility on the oil market is extremely high just now," Commerzbank analysts wrote in a note, Reuters reports. "This is due for the most part to the high speculative activity on the part of market participants."

Earlier this week, oil prices rallied on speculation that oil-producing countries may cooperate to curb production and raise prices.

Additionally, shares of Marathon Petroleum are declining after the oil refining and marketing company was downgraded to "neutral" from "overweight" at JPMorgan because of weak quarterly results from MPLX (MPLX), the master limited partnership formed by Marathon Petroleum, according to Barron's.

"[T]he MLP market has further melted down and MPLX's pro forma volume growth opportunities have slowed," analysts added, Barron's noted. "Marathon Petroleum may now be on the hook to provide even more support to MPLX."

Separately, Marathon Petroleum has a "hold" rating and a letter grade of C+ at TheStreet Ratings because of the company's strengths, such as reasonable valuation levels, largely solid financial position and notable return on equity, and its weaknesses, including poor profit margins and generally disappointing stock performance.

You can view the full analysis from the report here: MPC

TheStreet Ratings objectively rated this stock according to its "risk-adjusted" total return prospect over a 12-month investment horizon. Not based on the news in any given day, the rating may differ from Jim Cramer's view or that of this articles's author. 

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