It's a new feature in ADO.NET 2.0 and Sql Server 2005 that allows for multiple forward only read only result sets (MARS). Some databases have supported this functionality for a long time : Not Supported : DB2, MySql.Data, OLE DB provider [except Sql Server 2005 when using MDAC 9], SQLite, Obdc Supported : Sql Server 2005, Npgsql