Quarterly results from Exxon Mobil and ConocoPhillips on Thursday showed that while overall growth remained elusive, output rose in key basins in the United States where the oil and gas companies are spending heavily to grow crude production.

North American shale basins and the Gulf of Mexico are seen as more secure places for energy companies to invest because they typically offer a steady source of growth. Conoco said in December that more than half of its nearly $16 billion budget for 2013 will be spent in North America.

Exxon's U.S. oil and natural gas liquids production rose 2% in the first quarter, compared with an overall output decline of 3.5%.

"Lower production at Exxon is an ongoing trend, they need so many projects to come online to offset field decline," said Brian Youngberg, energy company analyst at Edward Jones. "But Conoco's shift toward the U.S. continues to proceed well."

Conoco said oil and gas production rose a combined 42% in the Bakken Shale in North Dakota and Texas' Permian Basin and Eagle Ford Shale. Conoco's total output from continuing operations edged 1% lower.

Fourth-largest U.S. oil company Occidental Petroleum said its daily domestic oil and gas production rose to a record 478,000 barrels of oil equivalent (boe), most of which was oil or natural gas liquids.

"Weak" beat

Exxon's quarterly profit edged up, helped by higher earnings in its chemicals business but oil and gas production fell.

Earnings per share for the world's largest publicly traded oil company topped Wall Street expectations but the gains largely came after a big stock buyback reduced the number of outstanding shares.

Analysts at Credit Suisse characterized it as a "weak" beat in a note to clients.

Exxon said it will lower its quarterly share buyback to $4 billion in the second quarter, below the $5 billion in the first quarter.

First-quarter profit for the world's largest publicly traded oil company was $2.12 per share. Analysts, on average, expected the Irving, Texas, company to report a profit of $2.05 per share.

Conoco's first-quarter results met Wall Street expectations and Occidental beat the Street, helped by higher profits in its midstream and marketing business and lower costs, analysts said.

Conoco had a first-quarter profit of $2.1 billion, or $1.73 per share, down from $2.9 billion, or $2.27 per share, a year earlier.

Occidental reported a first-quarter net profit of $1.36 billion, or $1.68 per share, compared with $1.56 billion, or $1.92 per share, a year earlier.

Excluding items, the Los Angeles company earned $1.69 per share, topping analysts' average estimate of $1.54 per share, according to Thomson Reuters I/B/E/S.