Governments buy about $9 trillion worth of goods and services a year, and their procurement policies are increasingly subject to international standards and institutional regulation including the WTO Plurilateral Agreement on Government Procurement, Open Government Partnership commitments and International Financial Institution procurement rules. These standards focus on transparency and open competition as key tools to improve outcomes. While there is some evidence on the impact of competition on prices in government procurement, there is less on the impact of specific procurement rules including transparency on competition or procurement outcomes. Using a database of World Bank financed contracts, we explore the impact of a relatively minor procurement rule governing advertising on competition using regression discontinuity design and matching methods. The rule does appear to have a small, positive impact on bidding levels, suggesting the potential for more significant and strongly enforced transparency initiatives to have a sizeable effect on procurement outcomes.