The requirements for cleaner engines and less fuel consumption force vehicle manufacturers to investigate new technologies on recovering from losses. As the main contributor to losses is the waste heat, studies are carried out to convert the waste heat to mechanical work. In this paper, an evaluation of Stirling engines is presented for waste heat recovery (WHR) from exhaust gases of a heavy-duty truck diesel engine. Maximum theoretical dimensionless shaft work for three types of Stirling engines are calculated and compared by optimizing selected parameters with a new dimensionless method. Results are used to size a WHR system that utilizes the thermal power of a commercial truck exhaust gas. Calculations done with exhaust gas temperatures measured during road tests show that, the WHR system with Beta-type Stirling engine is more effective than Alpha and Gamma types due to its higher power density. The WHR system presented provides more than 1.3% of ICE power output and about 1% reduction in fuel consumption, which offers Stirling engine as a reasonable option for WHR on heavy-duty truck engine.