Editor's Note: TheStreet ratings do not represent the views of TheStreet's staff or its contributors. Ratings are established by computer based on metrics for performance (which includes growth, stock performance, efficiency and valuation) and risk (volatility and solvency). Companies with poor cash flow or high debt levels tend to earn lower ratings in our model All three major indices are trading up today with the Dow Jones Industrial Average ( ^DJI) trading up 52 points (0.4%) at 12,867 as of Tuesday, Nov. 13, 2012, 11:54 AM ET. The NYSE advances/declines ratio sits at 1,426 issues advancing vs. 1,481 declining with 120 unchanged. The Basic Materials sector currently sits up 0.1% versus the S&P 500, which is up 0.5%. On the negative front, top decliners within the sector include Williams Partners ( WPZ), down 2.3%, PetroChina ( PTR), down 1.9%, Barrick Gold Corporation ( ABX), down 1.2%, Vale ( VALE), down 0.8% and Suncor Energy ( SU), down 1.1%. Top gainers within the sector include Emerald Oil ( EOX), up 264.9%, EOG Resources ( EOG), up 1.8%, Anadarko Petroleum ( APC), up 1.6%, Dow Chemical ( DOW), up 1.5% and Enterprise Products Partners ( EPD), up 1.4%. TheStreet Ratings group would like to highlight 3 stocks pushing the sector lower today: 3. MarkWest Energy Partners ( MWE) is one of the companies pushing the Basic Materials sector lower today. As of noon trading, MarkWest Energy Partners is down $2.42 (-4.9%) to $47.27 on heavy volume Thus far, 1.3 million shares of MarkWest Energy Partners exchanged hands as compared to its average daily volume of 547,100 shares. The stock has ranged in price between $46.92-$47.95 after having opened the day at $47.50 as compared to the previous trading day's close of $49.69. Markwest Energy Partners, L.P., together with its subsidiaries, engages in the gathering, processing, and transportation of natural gas in the southwest, Gulf Coast, and northeast regions of the United States. MarkWest Energy Partners has a market cap of $6.0 billion and is part of the energy industry. The company has a P/E ratio of 104.4, above the S&P 500 P/E ratio of 17.7. Shares are down 7.1% year to date as of the close of trading on Monday. Currently there are 8 analysts that rate MarkWest Energy Partners a buy, no analysts rate it a sell, and none rate it a hold. TheStreet Ratings rates MarkWest Energy Partners as a buy. The company's strengths can be seen in multiple areas, such as its revenue growth, impressive record of earnings per share growth, compelling growth in net income, expanding profit margins and notable return on equity. We feel these strengths outweigh the fact that the company shows weak operating cash flow. Get the full MarkWest Energy Partners Ratings Report now.