Occidental Petroleum (OXY) 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.Analysts' growing optimism on the earnings prospects of this oil and gas exploration and production company is driving estimates higher, 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. Our stock rating tool -- the Zacks Rank -- has this insight at its core.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.For Occidental, there has been strong agreement among the covering analysts in raising earnings estimates, which has helped push consensus estimates considerably higher for the next quarter and full year.The chart below shows the evolution of forward 12-month Zacks Consensus EPS estimate:12 Month EPSCurrent-Quarter Estimate RevisionsFor the current quarter, the company is expected to earn $0.51 per share, which is a change of +160.71% from the year-ago reported number.Over the last 30 days, three estimates have moved higher for Occidental compared to no negative revisions. As a result, the Zacks Consensus Estimate has increased 15.36%.Current-Year Estimate RevisionsFor the full year, the earnings estimate of $0.96 per share represents a change of +124.55% from the year-ago number.In terms of estimate revisions, the trend for the current year also appears quite encouraging for Occidental. Over the past month, two estimates have moved higher compared to no negative revisions, helping the consensus estimate increase 14.22%.Favorable Zacks RankThanks to promising estimate revisions, Occidental currently carries a Zacks Rank #2 (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 Occidental have attracted decent investments and pushed the stock 9.1% 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. Time to Invest in Legal Marijuana If you’re looking for big gains, there couldn’t be a better time to get in on a young industry primed to skyrocket from $17.7 billion back in 2019 to an expected $73.6 billion by 2027. After a clean sweep of 6 election referendums in 5 states, pot is now legal in 36 states plus D.C. Federal legalization is expected soon and that could be a still greater bonanza for investors. Even before the latest wave of legalization, Zacks Investment Research has recommended pot stocks that have shot up as high as +285.9%. You’re invited to check out Zacks’ Marijuana Moneymakers: An Investor’s Guide. It features a timely Watch List of pot stocks and ETFs with exceptional growth potential.Today, Download Marijuana Moneymakers FREE >>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 Occidental Petroleum Corporation (OXY): Free Stock Analysis Report To read this article on Zacks.com click here.