As a result of widespread interest EPA recently extended the comment deadline for proposed revisions to AP42 chapter 7, which specifies emission factors for organic liquid storage tanks. The AP42 emission factors are used to estimate emissions from specific industrial facilities and processes when no site-specific emissions data are available. They are used in a wide array of regulatory applications ranging from emissions inventories to permit applicability determinations to compliance and enforcement. The proposed changes for liquid storage tanks, which were prepared by the American Petroleum Institute, are extensive; in effect Chapter 7 is being rewritten. The results are unclear and may vary significantly among different types of tanks and facilities. Anyone who has relied on the AP42 factors for storage tanks, or may need to do so in the future, should evaluate the new emission factors and equations EPA is proposing. Comments are due by November 26.