Investors with an interest in Transportation - Shipping stocks have likely encountered both Scorpio Tankers (STNG) and Kirby (KEX). 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 Zacks Rank is a proven strategy that targets companies with positive earnings estimate revision trends, while our Style Scores work to grade companies based on specific traits.Currently, Scorpio Tankers has a Zacks Rank of #1 (Strong Buy), while Kirby has a Zacks Rank of #3 (Hold). This means that STNG's earnings estimate revision activity has been more impressive, so investors should feel comfortable with its improving analyst outlook. But this is just one piece of the puzzle for value investors.Value investors are also interested in a number of tried-and-true valuation metrics that help show when a company is undervalued at its current share price levels.The Value category of the Style Scores system identifies undervalued companies by looking at a number of key metrics. These include the long-favored P/E ratio, P/S ratio, earnings yield, cash flow per share, and a variety of other fundamentals that help us determine a company's fair value.STNG currently has a forward P/E ratio of 5.77, while KEX has a forward P/E of 30.40. We also note that STNG has a PEG ratio of 0.10. 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. KEX currently has a PEG ratio of 2.53.Another notable valuation metric for STNG is its P/B ratio of 1.18. The P/B ratio pits a stock's market value against its book value, which is defined as total assets minus total liabilities. For comparison, KEX has a P/B of 1.31.Based on these metrics and many more, STNG holds a Value grade of B, while KEX has a Value grade of C.STNG is currently sporting an improving earnings outlook, which makes it stick out in our Zacks Rank model. And, based on the above valuation metrics, we feel that STNG is likely the superior value option right now. How to Profit from the Hot Electric Vehicle Industry Global electric car sales in 2021 more than doubled their 2020 numbers. And today, the electric vehicle (EV) technology and very nature of the business is changing quickly. The next push for future technologies is happening now and investors who get in early could see exceptional profits. See Zacks' Top Stocks to Profit from the EV Revolution >>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 Scorpio Tankers Inc. (STNG): Free Stock Analysis Report Kirby Corporation (KEX): Free Stock Analysis Report To read this article on Zacks.com click here.