What happened

Shares of Hess Corp. (HES -2.81%) plunged in October, falling 23% for the month, according to data provided by S&P Global Market Intelligence. Fueling the sell-off was a double-digit decline in oil prices, which offset the company's strong third-quarter results.

So what

Oil prices tumbled more than 10% in October due to worries that market fundamentals were starting to weaken. Investors fretted over the continued rise in production at a time when demand growth has slowed because of higher oil prices and the impact of the trade war between the U.S. and China. That big drop in crude prices weighed on oil stocks like Hess last month.

An oil pump in a field.

Image source: Getty Images.

Last month's turmoil in the oil market hit Hess' stock hard. Because of that, Barclays upgraded the oil stock near the end of the month from underweight to equal weight, citing a more favorable valuation after the recent pullback. The bank noted that there's reason to be bullish on Hess given the long-term prospects of its oil development in Guyana with ExxonMobil (XOM -1.17%). The partners have now made nine discoveries totaling more than 4 billion barrels of recoverable resources. The massive find is one of the two main fuels Exxon plans to use to double its earnings and cash flow by 2025. Meanwhile, Hess sees it combining with the Bakken shale to grow its cash flow at a 25% compound annual growth rate through 2023 assuming oil averages $60 a barrel.

Hess ended last month on a high note after reporting strong third-quarter results. The company posted a profit of $0.38 per share, which shocked analysts who expected it to merely break even on the quarter. Fueling the company's surprising earnings was strong production growth in the Bakken shale -- which rose 14% compared to the year-ago period -- as well as higher oil prices and a big drop in costs.

Now what

Hess sold off along with oil prices last month, which is par for the course with oil stocks. However, it's worth noting that Hess' decline was particularly sharp, making its valuation much more compelling, especially given the growth it sees up ahead. That's why bargain-hunting investors might want to consider taking advantage of the sell-off to buy this oil stock for the long haul.