The United States Environmental Protection Agency (EPA) is investigating Reciprocating Internal Combustion Engines (RICE) to characterize engine emissions and catalyst control efficiencies of hazardous air pollutants (HAP). This document describes the results of HAP and particulate matter (PM) emissions testing conducted on a Caterpillar 3508 EUI diesel cycle, oil-fired, 4-stroke engine. Early in 1998, several industry and EPA representatives agreed that the Caterpillar 3508 EUI engine at the Colorado State University's (CSU) Engine and Energy Conversion Laboratory (EECL) is adequately representative of existing and new diesel cycle engines. The group agreed that a matrix of test results from testing conducted at the EECL could be used to develop Maximum Achievable Control Technology (MACT) standards for RICE. The group further agreed that an oxidation catalyst installed on the Caterpillar 3508 EUI could be used to determine the effectiveness of oxidation catalysts for these engines, and that the EPA could use the results from testing at CSU as the basis for developing the MACT standard for diesel cycle oil-fired engines.