Oil deepened its weekly decline amid the global glut as Goldman Sachs Group Inc. trimmed its price forecasts on signs the surplus will persist. Futures slid as much as 2 percent in New York, paring Thursday’s 4 percent gain. U.S. crude inventories climbed a second week through Sept. 4 to keep supplies about 100 million barrels above the five-year seasonal average, according to the Energy Information Administration. The world’s oversupply is even bigger than Goldman thought and that could drive prices as low as $20 a barrel, the bank said in an e-mailed report Friday. Oil has fluctuated since slumping below $40 a barrel almost three weeks ago as concern over growth in China fueled volatility in global markets. A Senate vote paved the way for President Barack Obama to ease financial penalties for doing business with Iran, which may allow an increase in oil exports. U.S. stockpiles continue […]