What: Shares of Oasis Petroleum Inc (NYSE:OAS) jumped more than 17% in early-morning trading after reporting better-than-expected second-quarter results after the market closed yesterday. That rally, however, fizzled quickly as the oil price reversed its own rally, falling to around $45 per barrel.

So what: Investors were initially elated by Oasis Petroleum's second-quarter results after it reported adjusted net income of $51.7 million, or $0.38 per share, which was a dime higher than analysts were expecting. There were dual drivers fueling that strong result, as production grew 15% year over year while lease operating expenses declined 19% from the year-ago quarter.

The company's outlook was also positive, as CFO Michael Lou stated in the press release: "Based on operational performance and cost savings in the first half of 2015, we were cash flow positive in the second quarter and expect to be cash flow positive for the remainder of 2015." Furthermore, he said that the company is now in a position to "be able to grow within cash flow in the current pricing environment in the coming years." Said another way, the company doesn't need higher oil prices to drive results.

Now what: That said, higher oil prices would certainly help Oasis and its peers, which is why investor enthusiasm is waning. Investors fear that oil companies can only cut so much out of costs, leaving more downside if oil continues to fall.