Starting with release 4.0, initialization properties are now resolved in the following order (for inspiration from the community, see this forum post):

• defaults are loaded from the classpath
• any overrides from transactions.properties (if found in the classpath) are applied
• any overrides from jta.properties (if found in the classpath) are applied
• any overrides in a properties file specified by the optional system property com.atomikos.icatch.file are applied
• any overrides set in a programmatic way are applied
• any overrides set a system properties are applied
• placeholder substitution is done for the resulting set of properties