The capabilities of a pilot-scale reciprocating biomass conversion reactor (RBCR) and its sensitivity to changes in various input parameters are examined. The RBCR is a 4-stroke diesel engine repurposed as a novel reactor to produce bio-oil by fast-pyrolysis of biomass. An external source powers the RBCR through the intake, compression/heating, expansion and exhaust strokes. Biomass is carried to the RBCR by an inert gas and is converted during compression as part of the compression work provides the heat of pyrolysis. A control-volume energy balance is coupled with a biomass decomposition mechanism from literature to predict the evolution of bio-products during compression and expansion strokes. The RBCR calculations are compared to experimental results from the state of the art considered to be a lab-scale fluidized-bed reactor (FBR). Calculations predict that the RBCR will increase the biomass throughput, and decrease the energy requirement for biomass conversion with a 6.8 times return on energy investment. The sensitivity analysis indicates the need for finely pulverized biomass for significant conversion, and highlights the versatility of the RBCR since operation parameters can be adjusted to achieve near complete conversion to bio-gas or to yield bio-oil up to 70% of biomass weight.