NEW YORK (CNN/Money) - ExxonMobil Corp. reported sharply lower second-quarter earnings Thursday that missed Wall Street expectations amid a downturn in its oil refining business.

The largest U.S. oil processor said it earned $2.64 billion, or 39 cents a share excluding items, down from $4.46 billion, or 65 cents, a year earlier. Analysts expected 46 cents a share, according to earnings tracker First Call.

Second-quarter revenue tumbled to $51 billion from $56.2 billion.

The company said capital and exploration spending jumped 20 percent to $3.4 billion in the quarter from $2.8 billion a year ago.

ExxonMobil (XOM: Research, Estimates) shares were higher early Thursday on the New York Stock Exchange.

ExxonMobil said depressed refining and marketing margins combined with lower crude oil and natural gas prices contributed to the disappointing results.

Earnings from crude oil and natural gas sales, considered "upstream" operations by oil companies, declined $697 million from the year-earlier quarter.

Earnings from refining and marketing operations, considered "downstream," declined $382 million from a year ago.

ExxonMobil also said negative overseas currency transactions, particularly in Argentina and Venezuela, combined with the effect of a weaker U.S. dollar on financing activities, shaved $100 million, or 2 cents a share, from second-quarter results.