This week, three Chemicals stocks are improving their overall ratings on Portfolio Grader. Each of these stocks is rated an “A” (“strong buy”) or “B” overall (“buy”).

Airgas (NYSE:ARG) ups its rating to a B (“buy”) this week after earning a C (“hold”) in the week before. Airgas is a distributor of industrial, medical, and specialty gases and hardgoods, such as welding equipment and supplies. In Portfolio Grader’s specific subcategory of Equity, ARG also gets an A. Shares of ARG have increased 5.1% over the past month, better than the 3.9% increase the S&P 500 has seen over the same period of time. For more information, get Portfolio Grader’s complete analysis of ARG stock.

Huntsman Corp. (NYSE:HUN) is making headway this week, with the company’s rating improving to an A (“strong buy”) from a B (“buy”) last week. Huntsman manufactures differentiated and commodity chemical products. The stock’s trailing PE Ratio is 7.80. For more information, get Portfolio Grader’s complete analysis of HUN stock.

Syngenta (NYSE:SYT) shows solid improvement this week. The company’s rating rises from a B to a A. Syngenta is an agribusiness that is engaged in the discovery, development, manufacture and marketing products designed to improve crop yields and food quality. Wall Street seems to agree with the upgrade and has propelled the stock up 7.5% over the past month. For more information, get Portfolio Grader’s complete analysis of SYT 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.