Information asummetry typically occurs where one party to a transaction has more or better information than another party. This creates and imbalance of power, resulting in ineffeciency, and is one of the major causes of market failure. When this concept is applied to public procurement, it is clear that opportunity for corruption are created by asymmetric information. This paper focuses on a case of public procurement in Thailand, namely the procurement of public buses by the Bangkok Metropolitan Transport Authority. Asymmetric information abounds, between the procuring agency, the would-be suppliers, and the watchdog agencies that include civil society. No allegation of corruption is implied, but careful scrutiny of procurement documents suggests that conditions, selection criteria, product specifications, and other details can be used to favor certain suppliers with impunity, to the detriment of society at large. The case shows that collaboration between watchdog agencies and professionals can reduce information gaps and make anti-corruption action more effective.