Dan LippePetral Worldwide Inc.HoustonAfter years of predictable seasonal variations in key elements of the supply-demand balance, the winter 2010-11 was another study in divergence from the norm.First, some yield accountants continued to misreport the composition of merchant sales of propylene and propane and distorted the reported volume of purity propane from Gulf Coast refineries. Second, instead of declining to accommodate the seasonal increase in retail propane demand, feedstock demand remained steady at summer volumes throughout the winter.Finally, Gulf Coast propane exports were higher during the winter than during the spring and summer. These and other issues are the primary focus...