A comparison of hydrocarbon columns against sealing faults and leaking faults demonstrates that larger columns are trapped against sealing faults.  Leaking faults have columns limited by JUXTAPOSED LITHOLOGY LEAK POINTS.  

Note that gas is not leakier than oil.  Larger gas than oil columns are trapped against sealing faults.  The maximum gas column trapped against a fault in this study is 2000 feet.

From the 

RISKING FAULT SEAL IN THE GULF COAST ATLAS (Seals International).