"INTRODUCTION This report addresses evaporative loss from internal floating-roof tanks (IFRTs) with closed vents@ a subject not currently addressed by API. Nomenclature is provided in Appendix A. The API Manual of Petroleum Measurement Standards Chapter 19@ Section 1 (19.1) addresses evaporative loss from fixed-roof tanks@ and specifically excludes fixed-roof tanks that have an internal floating roof (19.1.1.1). The API Manual of Petroleum Measurement Standards Chapter 19@ Section 2 (19.2) addresses evaporative loss from freely-vented internal floating-roof tanks@ and specifically excludes ""closed internal floating-roof tanks (that is@ tanks vented only through a pressure-vacuum relief vent@ blanketed with an inert gas@ vented to a vapor processing unit@ or otherwise restricted from being freely vented)"" (1d)."