With the S&P 500 (SNPINDEX:^GSPC) having set record highs earlier this week, investors are optimistic about the future. But with the beginning of third-quarter earnings season just a few weeks away, will negative surprises take the steam out of the bull-market rally? Let's take an early look at some projections on earnings.

A typical pattern
Investors have generally gotten more pessimistic about the prospects for earnings growth in the third quarter. According to figures from Zacks Investment Research, third-quarter estimates for the S&P 500 are expected to rise by just 1.4%. That growth estimate for the third quarter is down from the 3.3% investors expected at the beginning of August, and from as high as 7% early in 2013. Looking back even further, figures from Thomson Reuters show that analysts expected third-quarter S&P earnings of as much as $30.50 per share during early 2012. Since then, those projections have fallen to just above $27 per share -- a decline of more than 10%.

Before you adopt a gloom-and-doom approach, though, it's important to understand that pessimism usually runs rampant right before earnings season starts, giving way to more optimism as companies actually release their results. For instance, in both the first and second quarters of 2013, earnings expectations fell substantially in the months leading up to earnings season. But when the dust settled, earnings growth in both of those quarters came in between two and four percentage points higher than the gloomiest expectations coming into the quarter.

Watching for revenue
Although most investors focus on earnings, revenue growth will also be an important aspect of the health of the economy. A decline in overall sales of 0.7% in the second quarter was the worst performance since the aftermath of the financial crisis in late 2009. But Standard & Poor's expects third-quarter revenue to rise 4.8%, which would be the best level in more than a year and set the stage for continued strength in the fourth quarter.

Sector perspective
Among various sectors, telecom is likely to see the best earnings performance of any sector in the S&P 500. But as S&P notes, the reason is that Sprint (NYSE:S) left the S&P 500, taking its losses out of the overall calculation for the sector. With expectations of Sprint not returning to profitability until 2015 at the earliest, that somewhat-artificial move will benefit S&P telecoms.

Energy and financial stocks will bear the brunt of the pressure this quarter, with projected declines in earnings. Financials could see pressure from the impact of higher rates, with mortgage-financing revenue among major mortgage lenders likely to take an especially large hit.

For energy stocks, the same challenges of keeping production levels up will continue to pose a threat to earnings at major oil companies. ExxonMobil (NYSE:XOM) is expected to see earnings almost 8% when it reports, and given its huge influence on the S&P, its decline and that of peer ConocoPhillips will be enough to offset an expected 20%+ rise at rival Chevron (NYSE:CVX). Chevron has done a good job keeping its production levels up despite its size, and its efforts are paying dividends to shareholders. Perhaps more importantly, refining giant Valero Energy (NYSE:VLO) and its rivals are expected to see dramatic earnings drops as disappearing spreads between U.S. and world crude prices crush their profits.

Stay tuned
With earnings season almost upon us, it'll be interesting to see whether the usual trend toward a brighter picture will materialize this time around. With stocks having performed well despite the typical downgrades, even a normal set of relatively benign results could lead to another leg up for the S&P 500.