A deep dive into how to uncover the right oil stocks to invest in for the long-term. : The oil industry can be a challenging one for investors because oil prices are very volatile. In the last five years, crude plummeted from more than $100 a barrel all the way down to near $25 before bouncing back into the mid-$70s by the middle of 2018. That wild ride has caused investors in some oil stocks to lose a boatload of money, while others have unleashed a gusher of profits into their portfolio. Several factors separated the winners from the losers.