IRVING, Texas ( TheStreet) -- Exxon Mobil ( XOM) reported a 66% tumble in its second-quarter profit, missing Wall Street estimates along the way.

In what's becoming a familiar refrain among oil majors, Exxon blamed the performance on declining commodity prices coupled with slumping demand and thinning refining margins.

The world's biggest oil company said sales fell by nearly half to $74.5 billion from $138.1 billion in the year-earlier period.

Profit slipped to $3.95 billion, or 81 cents a share, in the second quarter as earnings in its three major segments -- upstream, downstream and chemicals -- fell off sharply. Excluding certain items, Exxon Mobil said it would have earned an adjusted 84 cents a share.

In the second quarter of 2008, Exxon Mobil posted profit of $11.68 billion, or $2.22 a share.

Analysts polled by Thomson Reuters forecast EPS of $1.02 and a top line of $71.3 billion.

Earnings from upstream operations, which include exploration and production activities, fell by 62%. Downstream earnings, which include its refining business, plunged 67% largely because of narrower refining margins. Domestic operations in the unit swung to a $15 million loss.

"Global economic conditions continue to impact the energy industry both in the volatility of commodity prices and reduced demand for products," Exxon Mobil Chairman Rex Tillerson said in a statement.

In morning trading Thursday, Exxon Mobil shares lost $1.10, or 1.5%, to $70.33.

-- Reported by Sung Moss in New York
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