http://docs.redhat.com/docs/en-US/JBoss_Enterprise_Application_Platform/5/html/Administration_And_Configuration_Guide/ch14s02.html

> <max-pool-size>
> The maximum number of connections allowed in the pool. Defaults to 20.

The actual default value is 10.

connector/src/main/org/jboss/resource/metadata/mcf/ManagedConnectionFactoryDeploymentMetaData.java

> @XmlElement(name="max-pool-size")
> @XmlJavaTypeAdapter(IntegerSystemPropertyXmlJavaTypeAdapter.class)
> private Integer maxPoolSize = 10;

I confirmed in both source code and runtime. It's 10 in JMX if I removed <max-pool-size> in *-ds.xml using EAP 5.1.1.