* 4th-qtr adj EPS $0.55 vs est $0.67
* Revenue rises 11 percent
* Exploration costs shoot up in United States
* Expects output available for sales to rise in 2013
Feb 6 Marathon Oil Corp reported a smaller-than-expected profit as exploration costs doubled in the United States, where the company is investing heavily in oil-rich shale formations.
Higher sales volumes of liquids from the Eagle Ford shale field in south Texas and the Bakken in North Dakota and Montana pushed up revenue by 11 percent.
Total exploration costs rose 70 percent to $238 million.
Marathon's shares, which closed at $34.72 on the New York Stock Exchange on Tuesday, fell about 2 percent in premarket trading.
Marathon, which also has operations in Canada, Norway, Poland and Indonesia, expects output available for sale in 2013 to be 6 percent to 8 percent higher, excluding Libya and Alaska.
Net output available for sales in 2012, excluding Libya, rose 8 percent to average at 427,000 barrels of oil equivalent (boe) per day.
The company sold its Alaskan assets last month and its production levels in Libya remain uncertain following the conflict in the region.
Net output available for sales in the fourth quarter, excluding Libya, rose 12 percent to average at 463,000 boe per day.
The Houston-based oil and gas company's profit fell 41 percent to $322 million, or 45 cents per share, in the fourth quarter from $549 million, or 78 cents per share, a year earlier.
Excluding one-time items, the company earned 55 cents per share. Revenue rose to $4.2 billion.
Analysts on average had expected earnings of 67 cents per share on revenue of $3.9 billion, according to Thomson Reuters I/B/E/S.