PurposeThe purpose of this paper is to analyze how local and central authorities choose between lowest price and more complex scoring rules when they design supplier-selection mechanisms for public procurements. Five hypotheses are tested: a high level of cost uncertainty and highly non-verifiable quality makes the use of the lowest-price supplier-selection method less likely. Organizational habits and transaction-cost considerations influence the choice of mechanism. Strong quality concerns make complex rules more likely.Design/methodology/approachThe analysis departures from normative theory (rational choice) and is based on the regression analysis and survey data comprising a gross sample of 40 contracting authorities and detailed information about 651 procurements.FindingsMore complex scoring rules are used more often when the authority is uncertain about costs and about delivered quality. Authority effects are also found to directly and indirectly influence the choice of supplier-selection method, suggesting that tendering design is partly driven by local habits and institutional inertia.Practical implicationsThe authors argue that, from a normative point of view, lowest price is an adequate method when the degree of uncertainty is low, for example, because the procured products are standardized and since quality can be verified. When there is significant cost uncertainty, it is better to use the so-called economically most advantageous tender (EMAT) method. (Preferably this should be done by assigning monetary values to different quality levels.) If there is significant uncertainty concerning delivered quality, the contracting authority should retain a degree of discretion, so as to be able to reward good-quality performance in observable but non-verifiable quality dimensions; options to extend the contract and subjective assessments of quality are two possibilities. The main findings are that EMAT and more complex scoring rules are used more often when the contracting authorities report that they experience substantial uncertainty concerning delivered quality and actual costs and that these factors tend to decrease the weight given to price, in line with the predictions. However, the authors also find that this result is mainly driven by variations between authorities, rather than by between-products variation for the same authority. This is from a training of professionals and regulation perspective of policy relevance.Social implicationsContract allocation based on habits rather than rational ground could implicate the waste of resources (tax payers money) as it adventures the matching of the preferences of the public sector (the objective, subject matter, of the procurement) and what the potential supplier offers in its tender.Originality/valueAlthough the principles for supplier selection are regulated by law they give the contracting authority substantial freedom in designing the scoring rule and in choosing what quality criteria to use. The tension between different objectives and the more general question whether the choices made by authorities reflect rational decision making or institutional inertia together motivate the current study. While the design of the supplier-selection mechanism is an important consideration in procurement practice, it has attracted relatively little attention from the academic community.