Costco Wholesale Corp. (COST) on Thursday reported quarterly earnings rose just 6 percent as steep oil prices cut into profits at its gas stations.

The largest U.S. warehouse club operator posted a net profit of $209.8 million, or 43 cents per share, in its fiscal third quarter ended May 8, compared with a profit of $198.7 million, or 42 cents per share, a year earlier.

Analysts, on average, expected a profit of 42 cents per share, according to Reuters Estimates. Costco said in April that earnings would be in the range of 41 cents to 43 cents per share, which was below Wall Street expectations at the time.

Shares of Costco rose 1.5 percent in trading Thursday.

Emme Kozloff, retail analyst with Sanford Bernstein, said gasoline prices have come down since Costco's April 22 warning, which eased margin pressure.

However, she said selling, general and administrative costs rose unexpectedly, and investors will be looking for details on what led to the increase when Costco hosts a conference call later on Thursday.

Costco has been under Wall Street pressure to cut costs, and had been making progress with four straight quarters of lower expenses, Kozloff said.

"The stock may be strong initially on the earnings upside to consensus, but as the (selling, general and administrative) pressure is scrutinized, the stock will likely come under pressure particularly given the recent run-up," she said.

Net sales for the quarter rose 10 percent to $11.75 billion, while stores open at least a year saw sales increase 7 percent from the year-ago quarter.

Costco, which competes with Wal-Mart Stores Inc.'s (WMT) Sam's Club and BJ's Wholesale Club Inc. (BJ), gave no details on its sales performance in Thursday's statement. The retailer said earlier this month that sales benefited from a weak dollar that boosted the value of international sales.

Costco operates gas stations at many of its 334 U.S. stores and usually charges less than traditional gas stations in hopes of using the discount to lure customers into its stores.

But its profits suffer when gas prices rise quickly because Costco replenishes gasoline supplies on a daily basis while most gas stations typically acquire their inventory weekly.

That means when energy prices soar, Costco must pay the higher price of the day while competitors are still selling supplies they bought for less a week earlier.

Analysts had hoped Costco would beat the lowered earnings expectations since gas prices have fallen since the company's profit warning, but they only edged out Wall Street estimates by 1 cent per share.

The results come one week after smaller rival BJ's said gasoline sales actually boosted its profit.

Analysts are expecting Costco to give more details on its gasoline business during its Thursday conference call.

Costco also lowered its full-year profit forecast in April because of the weak gasoline profits. Some on Wall Street think the outlook is too conservative and expect Costco to raise its fourth-quarter estimate.

Costco shares traded at $46.08 on Inet, up from Wednesday's Nasdaq closing price of $45.42.