This paper presents a comprehensive life cycle assessment (LCA) study of heavy duty off-road equipment. The machine studied here is a typical piece of diesel construction machinery equipped with the iT4 (interim Tier 4) certified diesel engine. Two life cycle impact assessment methods, Eco-Indicator 99 and IPCC 2007, are used to calculate the environmental impact and global warming potential associated with the machine's life cycle, from material extraction to end-of-life recycling and disposal. Due to fuel consumption and emissions, machine utilization during the usage phase is expected to account for most of the total environmental impact. However, the impact from usage can vary greatly, depending on how customers use the machine. To take into account various machine usage patterns, this LCA study performs two sensitivity analyses, varying the load factor and varying the fuel consumption rate, respectively.