The stock market continues to breach fresh all-time highs, yet many commodities, including oil, remain under pressure. There are likely a variety of factors for this, including lowered economic growth expectations thanks to the government shutdown and debt ceiling fiasco. As a result, oil has now declined to under $100 per barrel once again and gas currently sits at its 2013 low. This has stoked renewed fears over big oil earnings, which would surely be adversely affected by falling oil prices. Should energy investors worry?

Crimped margins mean pressured earnings
The benchmark U.S. oil price, West Texas Intermediate, is at its lowest level since July at about $97 per barrel. Furthermore, RBOB gasoline futures plunged on October 23 to $2.57 per gallon, the lowest price since November last year. While this is probably music to consumers' ears, it's bad news for energy investors. Many of the largest energy giants have struggled in recent months from harsh business conditions, meaning plunging oil and gas prices couldn't come at a less opportune time.

Energy behemoth ExxonMobil (XOM 0.23%) is still reeling from its last quarterly report, which showed that second-quarter net income fell a whopping 57%. Of course, acting as a buffer against falling oil prices is the fact that ExxonMobil's refining business will benefit from lower oil prices. Refining operations turn more favorable when oil prices fall, as margins are able to expand, thereby increasing profitability.

Meanwhile, BP (BP 0.71%) has made great strides in getting its business back on track following the tragic 2010 Gulf of Mexico spill, but falling oil prices may derail its progress. The company operates under a 10-point plan to build shareholder wealth over the long term, yet many of these initiatives are reliant on oil prices higher than where they are today. For instance, BP intends to generate a 50% increase in operating cash flow by 2014 as compared to 2011, but this projection is based on $100 per barrel oil. Therefore, if oil prices stay low (or worse, fall further), BP may not be able to make good on its promises.

In an even more precarious position is ConocoPhillips (COP 0.64%), which is much less 'integrated' than many of its big oil peers. That's because ConocoPhillips spun off its refining business last year, meaning investors are at particular risk from falling oil prices.

ConocoPhillips advises investors of the following annualized net income sensitivity: For every $1 per barrel change in West Texas Intermediate, the company's earnings stand to fluctuate between $30 million and $40 million. As a result, the roughly $10 per barrel shaved off West Texas Intermediate in just the past few weeks stands to carve out at least $300 million from ConocoPhillip's earnings power going forward.

Unfortunately for energy investors, the slide in commodity prices may not subside quickly. The fourth quarter is a traditionally slow period for energy demand, and rising stockpiles of oil and gas certainly aren't helping the matter. In the week ended October 18, U.S. oil inventories rose by more than five million barrels, roughly double what the market had expected.

The best course of action? Don't panic
As stock prices of the many energy companies, including ExxonMobil, BP, and ConocoPhillips, continue to hold up relatively well, investors may be wondering how long this can last in light of falling oil and gas prices. While a sense of caution is certainly appropriate in light of the over-arching industry headwinds, it's helpful to remember that each of these are well-run, highly profitable businesses.

It's impossible to predict the next direction in oil prices with any certainty, and as a result, investors simply need to trust that management of each of these companies is competent enough to steer their businesses through tough times. Moreover, Exxon, BP, and ConocoPhillips each pay hefty dividends that beat the yield on the broader market, which will help provide investors downside protection. As a result, investors would be wise to hold on and hope the plunge in commodity prices reverses sooner rather than later.