An increase in the use of conventional vehicles in combination with alternative fuel vehicles requires trucking carriers to make a decision on when to use a mixed fleet. The purpose of this article is to investigate how alternative fuel infrastructure and patterns of customer locations influence fleet compositions when minimizing routing costs. The variable-route vehicle refueling problem (VRVRP) for the mixed fleet is formulated as a mixed-integer programming model and solved with an optimization method. A logistic regression is then employed to assess the impacts of both the density of the alternative fuel infrastructure and the patterns of customer locations on the optimal fleet composition. Experimental results reveal that the right fleet mix decision is impacted by customer location patterns and available fuel infrastructure. While alternative fuel trucks were favored over conventional trucks with a dense alternative fuel infrastructure, the likelihood of mixed fleet use varied across different patterns, of customer demand locations. Further, our analysis suggests that shippers and trucking carriers should understand the relative benefits and constraints of different geographical dispersions of customers and densities of alternative fuel infrastructures when designing optimal delivery strategies.