X0101 EFFECT 33 LIVE 2013-09-26 16:00:00

S-4

0001397516 REX ENERGY CORP 333-190968 0001521777 Rex Energy I, LLC 333-190968-05 0001521781 Rex Energy Operating Corp. 333-190968-04 0001521859 Rex Energy IV, LLC 333-190968-03 0001521780 PennTex Resources Illinois, Inc. 333-190968-02 0001521778 RE Gas Development LLC 333-190968-01