It was the increasing US production in those states that was serving to bring national oil prices down.
OPEC (the world's largest oil cartel) deciding not to cut back on production, in spite of the oil supply and demand situation worldwide, likely had more than a little bit to bring down national oil prices also.
But it was our production that forced OPEC not to cut.
The only OPEC country that ever actually cuts production is Saudi Arabia, and right now they are in a war for market shares, so if they cut production, those markets needs would of just been filled by someone else. Prices would continue to decline, AND the Sauidi's would loose market share. With their growing welfare class, and the payoff necessary to keep them from revolting, the Saudi's had no real choice but to continue production levels.
OPEC is now less then 40% of the worlds oil production, which means the effectiveness of the cartel has been greatly degraded.