Shares Apache Corp. fell 4 percent as investors fretted the U.S. oil and gas company's exposure in Egypt, where mass protests against the government escalated Friday.

Since the protests began four days ago, shares of Apache have tumbled more than 8 percent.

"Apache Corporation confirms today its operations and oil and gas production remain unaffected by current events in Egypt," the company said in a statement posted Thursday on its website. "We continue to monitor developments as they occur."

In the third quarter, 20 percent of Houston-based Apache's oil and gas production came from its operations in Egypt, the company said.

Analysts at Houston-based energy investment bank Tudor Pickering Holt and Co said the Egyptian riots would continue to roil shares of Apache, but the stock should bounce back when calm is restored.

Shares of Apache tumbled 3.8 percent, or $4.41, to $111.92 in morning trading on the New York Stock Exchange. That compares with a slight decline in the CBOE index of oil companies.