Investors with an interest in Oil and Gas - Integrated - International stocks have likely encountered both BP (BP) and Exxon Mobil (XOM). But which of these two stocks presents investors with the better value opportunity right now? Let's take a closer look.Everyone has their own methods for finding great value opportunities, but our model includes pairing an impressive grade in the Value category of our Style Scores system with a strong Zacks Rank. The proven Zacks Rank puts an emphasis on earnings estimates and estimate revisions, while our Style Scores work to identify stocks with specific traits.BP and Exxon Mobil are both sporting a Zacks Rank of # 1 (Strong Buy) right now. Investors should feel comfortable knowing that both of these stocks have an improving earnings outlook since the Zacks Rank favors companies that have witnessed positive analyst estimate revisions. But this is just one factor that value investors are interested in.Value investors also try to analyze a wide range of traditional figures and metrics to help determine whether a company is undervalued at its current share price levels.Our Value category highlights undervalued companies by looking at a variety of key metrics, including the popular P/E ratio, as well as the P/S ratio, earnings yield, cash flow per share, and a variety of other fundamentals that have been used by value investors for years.BP currently has a forward P/E ratio of 7.08, while XOM has a forward P/E of 12.11. We also note that BP has a PEG ratio of 0.52. This popular figure is similar to the widely-used P/E ratio, but the PEG ratio also considers a company's expected EPS growth rate. XOM currently has a PEG ratio of 0.86.Another notable valuation metric for BP is its P/B ratio of 1. The P/B is a method of comparing a stock's market value to its book value, which is defined as total assets minus total liabilities. By comparison, XOM has a P/B of 1.55.These are just a few of the metrics contributing to BP's Value grade of B and XOM's Value grade of C.Both BP and XOM are impressive stocks with solid earnings outlooks, but based on these valuation figures, we feel that BP is the superior value option right now. Zacks' Top Picks to Cash in on Artificial Intelligence In 2021, this world-changing technology is projected to generate $327.5 billion in revenue. Now Shark Tank star and billionaire investor Mark Cuban says AI will create "the world's first trillionaires." Zacks' urgent special report reveals 3 AI picks investors need to know about today.See 3 Artificial Intelligence Stocks With Extreme Upside Potential>>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 BP p.l.c. (BP): Free Stock Analysis Report Exxon Mobil Corporation (XOM): Free Stock Analysis Report To read this article on Zacks.com click here.