U.S. oil and gas companies invested about $153.7 billion in drilling operations in 2012, working on an estimated 46,736 wells, according to the latest Joint Association Survey on Drilling Costs, released by the American Petroleum Institute (API).

Natural gas production in the United States is still developing and gathering speed, with a growing number of oil and gas wells being drilled, the API stated. Production is being driven by increased domestic investments that are helping the country meet its own energy needs and a larger proportion of the investment has been allocated to exploration and production both onshore and offshore, the association's statistics director Hazem Arafa said.

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Figures reveal that the total number of wells rose by 5.8 percent from 2011. Over the course of 2012, 61.1 percent of the total spending on drilling was dedicated to oil, while gas accounted for 30.7 percent. By contrast, in the previous year the proportions stood at 49.3 percent and 44.2 percent, respectively.

Shale drilling accounted for more than a third of the total expenditure (34.6 percent), down from 52.5 percent in 2011. The decline could be attributed to a drop in natural gas drilling mostly, whereas the number of new shale oil wells rose from 3,414 in 2011 to 3,619 in 2012. Investments in offshore operations went up to 7.1 percent of all oil and gas production expenditure in 2012, up from 6.5 percent in the previous year, the survey found.