Oil prices are a double-edged sword for the energy industry. High prices slow demand, but they still can boost profits, though the equation looks different to a refiner such as Philadelphia's Sunoco Inc. than to oil-rich competitors.

"They like to say that they don't widen their margins, but when you've got a $100 barrel of oil and your margin is 10 percent, you're making $10. When it's $50, you're making $5," said Joel Naroff, chief economist for TD Bank N.A.

Naroff said the whole energy sector faced lingering effects from this year's spike in oil prices above $147 a barrel, even though some analysts expect prices to stay in the $40 to $50 range next year.

"People are going to be much more cautious in their use of all types of energy," Naroff said.

Lower oil prices mean lower feedstock costs for much of the chemical industry, a boon to companies squeezed as commodity prices rose. But the slowdown also causes pain by cutting demand.       - Jeff Gelles