Exelon Corporation (NYSE: EXC) reported fourth-quarter results before the opening bell. The utility delivered adjusted operating earnings of $427 million, or $0.50 per share. This was below last year's fourth-quarter adjusted operating earnings of $547 million or $0.64 per share. Earnings also missed analysts' estimates by $0.03 per share.

Commenting on the quarter, CEO Christopher Crane said in a statement that, "Exelon delivered another year of strong operational performance and earnings within our guidance range, despite challenging market conditions." Among the company's challenges were lower realized energy prices across all of its regions.

Exelon's generation segment was among the hardest hit as the segment's adjusted operating profit fell by $100 million over last year's fourth quarter. The segment's average realized margin on all electric sales was $26.42 per megawatt-hour in this year's fourth quarter compared to $26.52 per megawatt-hour in the fourth-quarter of last year, which contributed to lower earnings.

Exelon's ComEd segment also saw its adjusted operating earnings fall year-over-year. ComEd's adjusted operating earnings fell to $109 million in the fourth-quarter of this year from $162 million in last year's fourth quarter. On the other hand, adjusted segment earnings at both PECO and BGE were up year over year. PECO saw its adjusted operating earnings rise to $103 million from $81 million, while BGE's adjusted operating earnings jumped to $48 million from $18 million.

Looking ahead to 2014, Exelon expects adjusted earnings to be in a range of $2.25 to $2.55 per share. That's in line with the $2.29 per share that analysts expect to see next year. However, that guidance does potentially point to a year-over-year decline in the company's earnings, as Exelon's adjusted earnings for 2013 were $2.50 per share. 

Matt DiLallo has no position in any stocks mentioned. The Motley Fool recommends Exelon. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.