Petchem producers unlikely to buy due to impurities in oil. Big middle distillates yield, less naphtha, LPG; wide variance in API gravities in assays, samples. Tests on samples of the same type of U.S. condensate now heading to South Korea and Japan have raised questions about the ultra-light crude's suitability for use in Asia, sources said, making some potential buyers wary about taking the oil. The uncertainty could delay a rapid build-up in the flow of U.S. condensate to Asia after the arrival of the first exports of U.S. crude in 40 years. Asian refiners and chemical producers will have to first determine the best use for the ultra-light oil before starting to buy in large volumes.