Oil prices on Tuesday slid more than three percent, to their lowest level in two months, to $40 a barrel under pressure from a stalling recovery in demand and planned production expansions by Opec that threaten to add to an existing glut of crude. Brent crude fell $2.18, or 5.2 percent, to $39.83 a barrel at 1400GMT, and earlier slipped to $39.61, the lowest since June 25. US West Texas ...