After three-and-a-half months of slow decline, the tipping point for a steeper drop came on Oct. 1, said Ray Carbone, president of broker Paramount Options Inc. That's when Saudi Arabia cut prices for its biggest customers. The reasons oil prices started sliding in June were hiding in plain sight: growth in U.S. production, sputtering demand from Europe and China, Mideast violence that threatened to disrupt supplies and never did.