Occidental Petroleum ( OXY) net income tumbled 70% thanks to what's becoming a familiar theme among oil company earnings: declining commodity prices. On Thursday, Occidental Petroleum said its earnings came to $682 million, or 84 cents per share, in the second-quarter, compared with $2.3 billion, or $2.78 a share, in the year-ago quarter. Revenue also nose-dived in the quarter, coming to $3.69 billion compared with $7.12 billion in the year-ago. The steep fall was led primarily by a slip in the bread-and-butter oil and gas segment, which saw revenues fall 50% to $2.73 billion. On average, Occidental said its realized price for a barrel of oil came to $52.97 in the quarter. But at the same time last year, in the midst of exploding oil prices, Occidental's realized price was $110.12 per barrel on average. Occidental's average realized gas prices also dropped by 71% in the same period. Analysts expected Occidental to show earnings at 80 cents with revenues pegged at $3.82 billion. Despite the sales drop, Occidental Petroleum still increased oil and gas sales production in the quarter, while global sales volumes also leaped 10% at 649,000 barrels of oil equivalent. Yesterday, Suncor ( SU) offered a similar assessment of its second quarter performance , pointing to declining prices and higher production.