MDAC 2.5 SDK - ODBC Driver for Oracle
The Microsoft ODBC Driver for Oracle is thread-safe; however, Oracle does not allow multiple concurrent statements on a single connection. The driver enforces this restriction. In other words, in multithreaded applications, although any thread can call into the ODBC Driver for Oracle at any time, the driver blocks any other thread from the driver on the same connection until the original thread leaves the driver.
The driver does not block if there are two statements on two different connections. However, if there is a single connection with two statements, there is potential for blocking.