Investors with an interest in Oil and Gas - Integrated - International stocks have likely encountered both Repsol SA (REPYY) and Exxon Mobil (XOM). But which of these two companies is the best option for those looking for undervalued stocks? 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.Both Repsol SA and Exxon Mobil have 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. However, value investors will care about much more than just this.Value investors analyze a variety of traditional, tried-and-true metrics to help find companies that they believe are undervalued at their current share price levels.Our Value category grades stocks based on a number of key metrics, including the tried-and-true P/E ratio, the P/S ratio, earnings yield, and cash flow per share, as well as a variety of other fundamentals that value investors frequently use.REPYY currently has a forward P/E ratio of 8.58, while XOM has a forward P/E of 16.39. We also note that REPYY has a PEG ratio of 0.22. This metric is used similarly to the famous P/E ratio, but the PEG ratio also takes into account the stock's expected earnings growth rate. XOM currently has a PEG ratio of 1.61.Another notable valuation metric for REPYY is its P/B ratio of 0.79. Investors use the P/B ratio to look at a stock's market value versus its book value, which is defined as total assets minus total liabilities. By comparison, XOM has a P/B of 1.61.These metrics, and several others, help REPYY earn a Value grade of B, while XOM has been given a Value grade of D.Both REPYY and XOM are impressive stocks with solid earnings outlooks, but based on these valuation figures, we feel that REPYY is the superior value option right now.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 Repsol SA (REPYY): Free Stock Analysis Report Exxon Mobil Corporation (XOM): Free Stock Analysis Report To read this article on Zacks.com click here. Zacks Investment Research