Searching for and selecting among design solutions is not an effortless task. The principle of least effort suggests people seek to minimize the amount of effort they apply towards completing their tasks. In the context of engineering design, it is conceivable that expending more effort on the design problem yields a design solution with greater performance. In this paper, we investigate the impact of incentives on motivating engineering designers to increase the amount of effort they apply to solving design problems. Specifically, we formulate an analytical model of effort provision towards design tasks to compare two incentive structures: a probabilistic incentive and a deterministic incentive. With the probabilistic incentive, a designers final reward or penalty is uncertain, e.g. it is uncertain if a proposed design solution will meet requirements. With the deterministic incentive, a designers final reward or penalty is tied directly to the quality of the design solution as it is presented, e.g. a proposed design solution meets requirements with a certain probability as the figure of merit and the designer is directly rewarded or penalized on producing a design solution with that figure of merit. We parameterize the proposed analytical model and perform a parameter study to determine which incentive produces a more optimal design solution in the parameter space. Results show that there is no one dominant incentive structure, and the preferred incentive structure depends on how intense the reward or penalty is and how a designer subjectively valuates his effort.