U.S. stocks moved to session lows by the middle of the day on Monday as crude oil hovered just above the $31 a barrel mark. Commodities resumed their slide on concerns Saudi Arabia will ramp up oil production despite oversupply. Caterpillar (CAT) shares slid after Goldman Sachs downgraded the stock to SELL from NEUTRAL. Analysts forecast sustained lower returns on capital driven by weaker global infrastructure spending. Halliburton (HAL) swung to a quarterly loss amid a severe downturn in the commodities market. The oilfield services provider said its bottom line was hit by severance payouts and asset write-offs during the quarter. Kimberly-Clark (KMB) slid after a disappointing quarter. TheStreet's Keris Lahiff has details from New York.