<Tr> <Th_colspan="3"> Annual owned production, 2009 . Source: </Th> </Tr> <P> In 2009, the production owned by the top ten companies was 52% of total US oil production . </P> <P> Each year, tens of thousands of wells are drilled in search of oil and gas in the U.S. In 2009, 36,243 wells were drilled . </P> <P> Top producing oil fields in the United States, 2013 </P>

Which region of the united states is not known for having large oil reserves