Oil prices fell after data showed a significant and unexpected increase in U.S. crude inventories for the second consecutive week, raising concerns about a decline in fuel demand. West Texas Intermediate crude futures dropped by 86 cents, or 1.1 percent, to $78.62, while Brent crude futures fell by 73 cents, or 0.9 percent, to $84.25, continuing to incur losses after a nearly 1 percent drop yesterday.