It's an admittedly overworked adage, especially in investing, but what goes up really does eventually come down. I expect that maxim to play out in spades for the integrated energy companies and refiners during the coming earnings season.

It's also the message from ConocoPhillips (NYSE:COP), which has warned that its third-quarter refining margins will be nearly slashed in half from their June-quarter levels. At the same time, crude oil prices have moved up steadily throughout the year, thereby boosting upstream realizations. But with the seizure of its assets in Venezuela, pipeline damage in the U.K., and planned maintenance at some of its facilities, the company says that it produced about 180,000 fewer barrels in the most recent quarter than it did in the June period.

I expect Conoco to be one of many big integrated companies to reflect such trends. Beyond that, with refinery margins down nearly 50% in the quarter, such major refiners as Tesoro (NYSE:TSO) and Valero (NYSE:VLO) will likely report substantially reduced earnings, both sequentially and year over year.

You probably recall that the second quarter saw expanded refining margins boost Big Oil's downstream profits, largely saving the day amid slightly lower year-over-year crude prices. That obviously won't happen in the third quarter. Despite crude prices now approaching $80 a barrel, firms like ExxonMobil (NYSE:XOM) and Chevron (NYSE:CVX) will probably join Conoco in reporting lower earnings across the board.

What does all this mean for investments in the energy group, whose earnings season will kick off on Oct. 19 with oilfield services leader Schlumberger (NYSE:SLB)? Very little, actually. While market conditions in energy can change quickly in just a few months, you're not investing for a quarter -- or at least, you shouldn't be.

I remain convinced that we're at or near the point where global crude oil demand will begin to outstrip supply, a gap that's likely to widen substantially as time marches on. You should be investing for that trend. It also makes me advise my Foolish friends that, especially with crude prices near record nominal levels, the producers mentioned above will become even more attractive on any sort of price pullback.

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Fool contributor David Lee Smith doesn't own any shares of the companies mentioned above. He does welcome your questions or comments. The Motley Fool has a disclosure policy.