For the current week, the overall ratings of three energy services stocks are worse, according to the Portfolio Graderdatabase. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

North American Energy Partners’ (NOA) rating falls this week to an F (“strong sell”), down from last week’s D (“sell”). North American Energy Partners is a resource services provider to oil and natural gas, and other natural resource companies, with a primary focus in the Canadian oil sands. For Portfolio Grader’s specific subcategory of Earnings Revisions, NOA also gets an F. To get an in-depth look at NOA, get Portfolio Grader’s complete analysis of NOA stock.

This is a rough week for Basic Energy Services, Inc. (BAS). The company’s rating falls to F from the previous week’s D. Basic Energy Services provides oil and gas drilling and production companies with a range of well site services. The stock gets F’s in Earnings Momentum, Earnings Revisions and Earnings Surprise. As of July 2, 2015, 21.9% of outstanding Basic Energy Services, Inc. shares were held short. For more information, get Portfolio Grader’s complete analysis of BAS stock.

Helix Energy Solutions Group, Inc.’s (HLX) rating weakens this week, dropping to an F versus last week’s D. Helix Energy Solutions is a marine contractor and operator of offshore oil and gas properties and production facilities. The stock receives F’s in Earnings Growth, Earnings Momentum and Earnings Revisions. Earnings Surprise and Sales Growth also get F’s. To get an in-depth look at HLX, get Portfolio Grader’s complete analysis of HLX 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.