When all was said and done, last month ended up being a decent one for the broad market. The S&P 500 (^GSPC -1.44%) ended August 1.9% above where it started. For a couple of S&P 500 stocks, however, the month was far better.

Chemical company Albemarle (ALB -6.28%) was August’s biggest S&P 500 winner, up a little more than 25% after China’s Contemporary Amperex Technology Company shut down operations at one of the world’s biggest lithium mines. Since Albemarle also owns and operates lithium mines, a diminished supply of the metal used to make electric vehicle batteries creates greater demand for Albemarle’s products.

That being said, the stock had the advantage of hitting the ground running early in the month. Albemarle’s second-quarter sales of $1.3 billion and non-GAAP (adjusted) per-share income of $0.11 reported at the very end of July were both better than expected, while the bottom line was considerably better than analysts’ estimates for a loss of around $0.84 per share.

Image source: Getty Images.

Shares of S&P 500 constituent and health insurer UnitedHealth Group (UNH 0.36%) rallied a little more than 24% last month, mostly in response to news that Warren Buffett’s Berkshire Hathaway had taken on a stake in the beaten-down stock.

Just keep the move in perspective. The stock’s still down 48% from April’s peak thanks to the 60% sell-off from that high to the multiyear low hit in early August following a disappointing first-quarter report and subsequent reductions for its full-year earnings outlook. The company’s now only looking for 2025 earnings of “at least $16.00” per share, well down from guidance of between $29.50 and $30.00 per share as of the end of last year. Unexpectedly high costs (particularly for its Medicare Advantage plans) are the chief culprit.

While both gains are impressive, in and of themselves, they aren’t reason enough to step in. You’ll still want to be sure these companies are actually worth owning before buying into either of them.