The proven Zacks Rank system focuses on earnings estimates and estimate revisions to find winning stocks. Nevertheless, we know that our readers all have their own perspectives, so we are always looking at the latest trends in value, growth, and momentum to find strong picks.

Of these, perhaps no stock market trend is more popular than value investing, which is a strategy that has proven to be successful in all sorts of market environments. Value investors rely on traditional forms of analysis on key valuation metrics to find stocks that they believe are undervalued, leaving room for profits.

Luckily, Zacks has developed its own Style Scores system in an effort to find stocks with specific traits. Value investors will be interested in the system's "Value" category. Stocks with both "A" grades in the Value category and high Zacks Ranks are among the strongest value stocks on the market right now.

One company to watch right now is Northern Oil and Gas (NOG). NOG is currently holding a Zacks Rank of #2 (Buy) and a Value grade of A. The stock is trading with a P/E ratio of 6.53, which compares to its industry's average of 9.79. Over the past year, NOG's Forward P/E has been as high as 7.64 and as low as 4.55, with a median of 5.37.

Another valuation metric that we should highlight is NOG's P/B ratio of 1.87. The P/B ratio is used to compare a stock's market value with its book value, which is defined as total assets minus total liabilities. This stock's P/B looks attractive against its industry's average P/B of 2.35. NOG's P/B has been as high as 2.70 and as low as 1.56, with a median of 2.02, over the past year.

Value investors also frequently use the P/S ratio. This metric is found by dividing a stock's price with the company's revenue. This is a popular metric because sales are harder to manipulate on an income statement, so they are often considered a better performance indicator. NOG has a P/S ratio of 1.89. This compares to its industry's average P/S of 2.07.

Finally, investors will want to recognize that NOG has a P/CF ratio of 3.26. This figure highlights a company's operating cash flow and can be used to find firms that are undervalued when considering their impressive cash outlook. NOG's P/CF compares to its industry's average P/CF of 7.84. Over the past year, NOG's P/CF has been as high as 3.79 and as low as 2.18, with a median of 3.20.

These are only a few of the key metrics included in Northern Oil and Gas's strong Value grade, but they help show that the stock is likely undervalued right now. When factoring in the strength of its earnings outlook, NOG looks like an impressive value stock at the moment.