Even though the energy sector has sharply outperformed the broader market this year, there are still pockets of opportunity for investors looking for long-term buys, according to Goldman Sachs. The sector is up about 63% on the year, boosted by high oil prices, while the S & P 500 is still down about 19% year to date. But that's only this year – it's not a long-term trend. "If one zooms out and looks back over the last five years the XLE still has underperformed the S & P by 16% before the dividend," Goldman Sachs analyst Neil Mehta wrote in a Thursday note. "We continue to believe that mean reversion is an effective strategy for identifying potential candidates in the sector, particularly if one looks at a longer-time horizon given the long cycle nature of the business." The firm has identified six stocks that have underperformed over the last five years and are good candidates for "positive mean reversion." Favorite long-term energy buys Every stock on Goldman's list is buy rated, including EOG Resources , which the firm recently upgraded to due to improving capital, upside from new plays and strong capital efficiency and execution. "We believe EOG has underperformed as investors have been concerned about the lack of clarity around return of capital (this is better known) and perception of resource degradation in plays such as the Eagle Ford," said Mehta. "We see 18% total return to our 12-month price target to EOG." The firm sees an even larger upside for Ovintiv , which it thinks could surge 40% in the next 12 months. In addition, the company is trading at a deep discount to its peers, making it a potentially solid buy for investors looking to hold long-term. Oil services, represented on the list by Halliburton , "has been a notable laggard in the last five years given overcapacity, weak pricing, lackluster returns of capital and limited investor interest," said Mehta. "That said, investor engagement in the space is meaningfully improving, especially on the back of a strong Q3 set of results across companies," he added. While Halliburton has underperformed, it's turning around with consistent and strong earnings execution. For Phillips 66 , there's an attractive set up into its Nov. 9 analyst day, according to the note. Goldman sees a 13% upside to its 6-month price target of $109. Exxon Mobil has been a strong performer this year but is on the list because it's lagged its peer, Chevron, by 18% in the last five years and by 60% in the last decade. "That said, we believe we are in a structural period where we still prefer Exxon vs. Chevron," Mehta wrote, adding that they see three structural advantages for the company – a greater refining footprint, strong growth assets and an 8% upside to Goldman's price target. Suncorcar has been an underperformer but offers an 18% upside to Goldman's 12-month price target. "We also see a series of catalysts that can improve sentiment including clarity on CEO, strong refining margins, protection from Western Canadian crudes and ongoing returns of capital," Mehta wrote. — CNBC's Michael Bloom contributed to this report.