The grades of 11 oil and gas stocks are on the rise this week on Portfolio Grader. Each of these stocks is rated an “A” (“strong buy”) or “B” overall (“buy”).

Chesapeake Midstream Partners’ (CHKM) grade is moving up to a B (“buy”) this week from last week’s C (“hold”). Chesapeake Midstream Partners owns, operates, develops, and acquires natural gas, natural gas liquids, and oil gathering systems, as well as other midstream energy assets in the United States. For more information, get Portfolio Grader’s complete analysis of CHKM stock.

PVR Partners, L.P. (PVR) improves from a C to a B rating this week. PVR Partners owns and operates a network of natural gas pipelines and processing plants that provide gathering, transportation, compression, processing, dehydration and related services to natural gas producers. For more information, get Portfolio Grader’s complete analysis of PVR stock.

Cheniere Energy Partners, L.P. (CQP) is seeing ratings go up from a C last week to a B this week. Cheniere Energy owns and operates the Sabine Pass liquefied natural gas (LNG) terminal located in western Cameron Parish, Louisiana on the Sabine Pass Channel. For more information, get Portfolio Grader’s complete analysis of CQP stock.

The rating of Petrobras Argentina SA Sponsored ADR Class B (PZE) moves up this week, rising from a C to a B. Petrobras Argentina explores for, produces, refines, and transports oil and natural gas in South America. Shares of the stock have been trading at an exceptionally rapid pace, up twofold from the week prior. For more information, get Portfolio Grader’s complete analysis of PZE stock.

Valero Energy Corporation’s (VLO) ratings are looking better this week, moving up to a B from last week’s C. Valero is an independent petroleum refiner and marketer. For more information, get Portfolio Grader’s complete analysis of VLO stock.

This week, Teekay Tankers Ltd. Class A (TNK) is showing good progress as the company’s rating jumps from a B (“buy”) last week to an A (“strong buy”). Teekay Tankers owns oil tankers and transports crude oil. For more information, get Portfolio Grader’s complete analysis of TNK stock.

This is a strong week for Vertex Energy, Inc. (VTNR). The company’s rating climbs to B from the previous week’s C. Vertex Energy is a middle market consolidator, refiner and re-refiner of distressed petroleum streams, such as used oil, transmix, fuel oils and off-specification commercial chemical products. Shares of the stock have been changing hands at an unusually rapid pace, three times the rate of the week prior. For more information, get Portfolio Grader’s complete analysis of VTNR stock.

Marathon Petroleum Corporation (MPC) earns a B this week, jumping up from last week’s grade of C. Marathon Petroleum is a supplier of gasoline and distillates to resellers and consumers. Shares of the stock have been changing hands at an unusually rapid pace, twice the rate of the week prior. For more information, get Portfolio Grader’s complete analysis of MPC stock.

Westmoreland Coal Company (WLB) shows solid improvement this week. The company’s rating rises from a C to a B. Westmoreland Coal mines coal, which is used to produce electric power, and owns power-generating plants. For more information, get Portfolio Grader’s complete analysis of WLB stock.

This week, U.S. Energy Corp. (USEG) pushes up from a C to a B rating. U. S. Energy explores for oil and natural gas. For more information, get Portfolio Grader’s complete analysis of USEG stock.

This week, Euronav NV’s (EURN) ratings are up from a C last week to a B. Shares of the stock have been trading at an exceptionally rapid pace, up twofold from the week prior. For more information, get Portfolio Grader’s complete analysis of EURN stock.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.