While the proven Zacks Rank places an emphasis on earnings estimates and estimate revisions to find strong stocks, we also know that investors tend to develop their own individual strategies. With this in mind, we are always looking at value, growth, and momentum trends to discover great companies.Looking at the history of these trends, perhaps none is more beloved than value investing. This strategy simply looks to identify companies that are being undervalued by the broader market. Value investors use a variety of methods, including tried-and-true valuation metrics, to find these stocks.In addition to the Zacks Rank, investors looking for stocks with specific traits can utilize our Style Scores system. Of course, value investors will be most interested in the system's "Value" category. Stocks with "A" grades for Value and high Zacks Ranks are among the best value stocks available at any given moment.CrossAmerica Partners (CAPL) is a stock many investors are watching right now. CAPL is currently holding a Zacks Rank of #2 (Buy) and a Value grade of A.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. CAPL has a P/S ratio of 0.15. This compares to its industry's average P/S of 0.37.Finally, our model also underscores that CAPL has a P/CF ratio of 5.72. This metric focuses on a firm's operating cash flow and is often used to find stocks that are undervalued based on the strength of their cash outlook. This stock's P/CF looks attractive against its industry's average P/CF of 6.80. Within the past 12 months, CAPL's P/CF has been as high as 8.51 and as low as 5.65, with a median of 7.23.Another great Oil and Gas - Refining and Marketing - Master Limited Partnerships stock you could consider is Sunoco (SUN), which is a # 2 (Buy) stock with a Value Score of A.Furthermore, Sunoco holds a P/B ratio of 4.40 and its industry's price-to-book ratio is 3.11. SUN's P/B has been as high as 5.76, as low as 3.69, with a median of 4.44 over the past 12 months.These are just a handful of the figures considered in CrossAmerica Partners and Sunoco's great Value grade. Still, they help show that the stock is likely being undervalued at the moment. Add this to the strength of its earnings outlook, and we can clearly see that CAPL and SUN is an impressive value stock right now. Zacks Names "Single Best Pick to Double" From thousands of stocks, 5 Zacks experts each have chosen their favorite to skyrocket +100% or more in months to come. From those 5, Director of Research Sheraz Mian hand-picks one to have the most explosive upside of all. It’s a little-known chemical company that’s up 65% over last year, yet still dirt cheap. With unrelenting demand, soaring 2022 earnings estimates, and $1.5 billion for repurchasing shares, retail investors could jump in at any time. This company could rival or surpass other recent Zacks’ Stocks Set to Double like Boston Beer Company which shot up +143.0% in little more than 9 months and NVIDIA which boomed +175.9% in one year.Free: See Our Top Stock and 4 Runners Up >>Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report CrossAmerica Partners LP (CAPL): Free Stock Analysis Report Sunoco LP (SUN): Free Stock Analysis Report To read this article on Zacks.com click here. Zacks Investment Research