A number of oil services stocks are falling after the leader in the sector, Schlumberger (SLB), stated on slides for the Howard Weil Conference that activity in North America has been below expectations in the first quarter. The company's customers have activated fewer rigs on the continent than they had previously indicated, Schlumberger explained. Schlumberger also stated that it was temporarily reducing its activity in Venezuela due to "collection issues." The company forecast that its earnings per share would grow by double digit percentage levels this year, in-line with its previous outlook, as long as North American land activity and prices meet its previous forecast and issues resolve in Venezuela. Meanwhile, the company forecast that demand for oil would increase just 1% in 2013 compared to 2012. The increase will be driven by developing markets, with China generating 50% of the growth, Schlumberger stated. In mid-afternoon trading, Schlumberger fell 3% to $77, Baker Hughes (BHI) gave back 2% to $47, Weatherford (WFT) lost 1.5% to $12, and Halliburton (HAL) lost 1.6% to $41.23.