Hi, I updated my test code to use your way of creating the Knowledge Base (using KieBase) and I have the exact same results. Does anyone have an idea why this is still failing? Furthermore, I think the way I was initializing my rules is also supported by Drools 6, because it's almost copied line by line from the Official Drools API page: https://docs.jboss.org/drools/release/6.0.1.Final/kie-api-javadoc/ / A Typical example to load a rule resource. KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder(); kbuilder.add( ResourceFactory.newUrlResource( url ), ResourceType.DRL ); if ( kbuilder.hasErrors() ) { System.err.println( builder.getErrors().toString() ); } KnowledgeBase kbase = KnowledgeBaseFactory.newKnowledgeBase(); kbase.addKnowledgePackages( builder.getKnowledgePackages() ); StatefulKnowledgeSession ksession = knowledgeBase.newStatefulKnowledgeSession(); ksession.insert( new Fibonacci( 10 ) ); ksession.fireAllRules(); ksession.dispose();/ Best, Josep -- View this message in context: http://drools.46999.n3.nabble.com/Rules-don-t-execute-using-MVEL-syntax-i... Sent from the Drools: User forum mailing list archive at Nabble.com. _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users