NEW YORK (TheStreet) -- Shares of Marathon Oil (MRO - Get Report) are advancing 4.98% to $12.86 in mid-afternoon trading on Monday as oil prices reached a six-month high.

Crude oil (WTI) is spiking 3.16% to $47.67 per barrel and Brent crude is up 2.55% to $49.05 per barrel this afternoon.

Oil prices are rallying on concerns about supply outages in Nigeria and Venezuela as Goldman Sachs (GS), which has been bearish on oil prices, seemed more positive on the market, Reuters reports.

"The oil market has gone from nearing storage saturation to being in deficit much earlier than we expected," the investment bank said in a note.

"The market likely shifted into deficit in May...driven by both sustained strong demand as well as sharply declining production," Goldman added.

The firm now expects oil prices to increase to $50 per barrel in the second half of the year, above its April 22 outlook for prices trading between $40 and $45 in the second half, the Wall Street Journal noted.

Marathon Oil is a Houston-based exploration and production company.

Separately, TheStreet Ratings Team has a "Sell" rating with a score of D on the stock.

The company's weaknesses can be seen in multiple areas, such as its poor profit margins, weak operating cash flow, generally disappointing historical performance in the stock itself, disappointing return on equity and feeble growth in its earnings per share.

Recently, 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.

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