This report summarizes the benefits and costs associated with the National Emissions Standard for Hazardous Air Pollutants (NESHAP) for the Reciprocating Internal Combustion Engines (RICE) source category. This source category includes spark ignition engines that operate generally with natural gas and compression ignition engines that operate with diesel fuel, and can be classified as two-stroke, or four-stroke engines. They are also classified by the richness of the fuel mix: rich burn or lean burn. The affected RICE units operate in a variety of markets and service industries. For instance, some are typically used along natural gas pipelines to provide adequate pressure to transmit fuel through the pipeline. Others are also used to provide power in a remote area of an operation in industries such as health services, energy generation, oil and gas extraction, and quarrying of non-metallic minerals. The NESHAP for RICE will impact existing and new sources of RICE units and is expected to reduce HAP emissions by 5,600 tons per year by the year 2005 due to controls required to achieve the MACT floorthe minimum level of control mandated by the Clean Air Act. The controls applied to RICE units will also achieve annual reductions of criteria pollutants, including: 234,400 tons of carbon monoxide (CO) per year by 2005, and 167,900 tons of nitrogen oxides (NOx) per year, and 3,700 tons of particulate matter (PM (sub 10)).