Oil headed for the biggest weekly decline since early April on increasing evidence that a global economic slowdown is destroying demand, with prices near the lowest level in six months. West Texas Intermediate were little changed below $89 a barrel on Friday, and was 10% lower for the week. US gasoline consumption has softened while crude stockpiles have increased. Supply from Libya has picked up, helping shrink key oil futures time-spreads and ease the tightness in the market.