Diamondback Energy (FANG) could be a solid addition to your portfolio given a notable revision in the company's earnings estimates. While the stock has been gaining lately, the trend might continue since its earnings outlook is still improving.The upward trend in estimate revisions for this energy exploration and production company reflects growing optimism of analysts on its earnings prospects, which should get reflected in its stock price. After all, empirical research shows a strong correlation between trends in earnings estimate revisions and near-term stock price movements. This insight is at the core of our stock rating tool -- the Zacks Rank.The five-grade Zacks Rank system, which ranges from a Zacks Rank #1 (Strong Buy) to a Zacks Rank #5 (Strong Sell), has an impressive externally-audited track record of outperformance, with Zacks #1 Ranked stocks generating an average annual return of +25% since 2008.Consensus earnings estimates for the next quarter and full year have moved considerably higher for Diamondback, as there has been strong agreement among the covering analysts in raising estimates.The chart below shows the evolution of forward 12-month Zacks Consensus EPS estimate:12 Month EPSCurrent-Quarter Estimate RevisionsThe company is expected to earn $0.76 per share for the current quarter, which represents a year-over-year change of -60.62%.Over the last 30 days, the Zacks Consensus Estimate for Diamondback has increased 7.91% because three estimates have moved higher while two have gone lower.Current-Year Estimate RevisionsFor the full year, the earnings estimate of $3.04 per share represents a change of -56.13% from the year-ago number.The revisions trend for the current year also appears quite promising for Diamondback, with three estimates moving higher over the past month compared to two negative revisions. The consensus estimate has also received a boost over this time frame, increasing 39.12%.Favorable Zacks RankThe promising estimate revisions have helped Diamondback earn a Zacks Rank #1 (Strong Buy). The Zacks Rank is a tried-and-tested rating tool that helps investors effectively harness the power of earnings estimate revisions and make the right investment decision. You can see the complete list of today's Zacks #1 Rank (Strong Buy) stocks here.Our research shows that stocks with Zacks Rank #1 (Strong Buy) and 2 (Buy) significantly outperform the S&P 500.Bottom LineWhile strong estimate revisions for Diamondback have attracted decent investments and pushed the stock 7.2% higher over the past four weeks, further upside may still be left in the stock. So, you may consider adding it to your portfolio right away.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 Diamondback Energy, Inc. (FANG): Free Stock Analysis Report To read this article on Zacks.com click here. Zacks Investment Research