In order to determine whether proprietary standardization or open standardization creates more value for a firm involved in standardization, a study was conducted to examine the market value of standardization initiatives. Data were drawn from 148 XML schema standardization initiatives collected from the Lexis-Nexis database during the period January 1999 to December 2003. Findings indicate that financial markets respond positively to announcements of proprietary XML schema standardization, but not to those of open XML schema standardization. Findings also indicate that investors do not develop a preference for open standards over time.