The high cost of oil is hurting ... oil companies?

The shrinking margins are affecting companies that produce and process oil as well as those focused only on refining. Chevron and ConocoPhillips — both integrated companies that find, pump, ship and refine oil, then sell the resulting products — recently warned that third-quarter refining profits will fall sharply.

Valero Energy Corp., the nation’s largest independent oil refiner, joined the warning parade, as did Marathon Oil Corp., a smaller integrated oil company.

It’s easy to understand why a company like Valero is affected by low refining margins; it has to buy the oil it processes. But why are integrated companies which produce oil also affected?

“They don’t actually refine their own oil,” explained Ben Tsocanos, director of ratings services at Standard & Poor’s in New York.

But all oil companies pay attention to market forces, which means some refiners may decide to sit out the market for a while. That could lead to a drop in gasoline supplies and higher pump prices.

“At some point, there’s going to have to be a situation where refiners who are down for maintenance will look at the margins and say, hey, let’s stay down,” Ritterbusch said.

Despite lower refining margins, investors tend to flock to oil company stocks when oil prices are rising. Shares of Exxon Mobil, the world’s biggest publicly traded oil company, have traded in record territory of late.

In a research note Friday, Bank of America Securities analyst Daniel Barcelo said Exxon Mobil’s businesses and cash flows were robust, and its shares were trading at a discount. Barcelo reiterated his “buy” rating and $98 per share target price.

Exxon Mobil shares ended the week at $93.48, up 12.2 percent since its most recent low on Aug. 16. Chevron shares have gained 12.3 percent over the same period, and ConocoPhillips shares rose 10.9 percent.

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