X0101 EFFECT 33 LIVE 2016-05-31 15:00:00

S-4

0001397516 REX ENERGY CORP 333-211293 0001521777 Rex Energy I, LLC 333-211293-05 0001521781 Rex Energy Operating Corp. 333-211293-04 0001521778 RE Gas Development LLC 333-211293-03 0001521780 PennTex Resources Illinois, Inc. 333-211293-02 0001521859 Rex Energy IV, LLC 333-211293-01