Big profits for Big Oil, but sector shares tumble

Shares of the industry's biggest players were hit hard amid a global slowdown and extraordinarily high expectations.

Since Exxon Mobil Corp. reported the biggest profit from operations ever by any U.S. corporation, it's shares have fallen more than 5 percent.

After Royal Dutch Shell PLC reported second-quarter net profits rose 33 percent from a year ago to a company record $11.6 billion in July, its shares have fallen 20 percent.

Investors are concerned about a global slowdown that could eat away at the appetite for energy, both for consumers and for businesses.

Major refiners fared poorly as well, squeezed by refining margins due to the cost of crude they had to buy to make gasoline.

But share prices held up comparatively well, even as profits declined.

Valero Energy Corp., North America's largest refiner, saw shares decline by just over $2 during the quarter.