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In September 2016, two classes of stocks outperformed everything else by a wide margin. Partly thanks to surging oil prices, three of the S&P 500's top five performers that month came from the energy industry. The other two tickers in that elite quintet were hard-drive builders, lifted by a rebounding market for PC systems.

Let's have a closer look at September's best performers.

APA Chart

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In a series of jumps and drops, the price of crude oil rose more than 8% last month. The tide of global political pressure turned as the OPEC consortium agreed to cut production by 1.5 million barrels per day. A rising tide lifts all boats, and oil stocks were generally very kind to their owners in September. For major independent oil producer Anadarko Petroleum (NYSE:APC), this was the main story behind September's rising share prices.

But wait -- there's more.

On top of that strong foundation, Apache Corporation (NASDAQ:APA) announced the discovery of a newly discovered 3 billion-barrel reserve of shale oil. Apache's stock rose 7% on that finding alone.

And for Spectra Energy, oil prices hardly even mattered. Here, the big boost arrived when fellow energy pipeline operator Enbridge (NYSE:ENB) announced an all-stock merger with Spectra to create a titan of the energy midstream industry.

After several months of plunging oil prices, the energy sector is thirsty for a serious rebound. Many smaller companies have found merger partners to stave off a bitter end -- or gone out of business altogether. Weak balance sheets are being put to the ultimate test here, and the sector is consolidating in response.

Signs of life in PCs

Meanwhile, in the computer hardware corner, rumors of the PC's death turned out to be greatly exaggerated.

Storage giant Western Digital (NASDAQ:WDC) got the ball rolling in early September. That's when the company raised its first-quarter guidance, reflecting two positive trends: the integration with recently acquired peer SanDisk that's running ahead of schedule -- and a PC industry that's showing signs of recovery.

That announcement lifted Western Digital shares 13% higher overnight, and the stock has held steady at this elevated level.

Arch rival Seagate (NASDAQ:STX) took a smaller step up that day but followed up with another surge as private-equity firm ValueAct Capital invested more than $400 million in the company. ValueAct is now one of Seagate's largest shareholders, holding 4% of the company's shares. The firm explained its investment with a desire to take advantage of "attractive long-term secular trends" around Seagate's business.

Other technology businesses and independent market watchers have only amplified the message found in Western Digital's tea leaves. The PC market seems is not quite dead yet, and it seems ready to stick around for a while.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.