An estimated $153.7 billion was spent on oil and natural gas drilling in the United States in 2012, up 23.1% from 2011, according to a new report issued by the American Petroleum Institute (API). Significantly, it revealed that spending on shale drilling fell during the period.

The Joint Association Survey on Drilling Costs reported that 46,736 oil and gas wells were drilled in 2012, an increase of 5.8% from 2011 levels. Expenditures on oil accounted for 61.1% of all drilling costs last year, up from 49.3% in 2011, while gas expenditures represented 30.7% of drilling costs in 2012, down from 44.2% in 2011.

API estimated that expenditures on shale drilling fell by nearly 18% over the period to 34.6% of drilling costs in 2012 from 52.5% in 2011. Most of the decline occurred in natural gas drilling, while the number of new shale oil wells increased to 3,619 in 2012 from 3,414 in 2011, it said.

Natural gas production still remains at historic highs, API said. “But we’re seeing that new production is following the market, where the demand for oil is driving growth,” said API’s Hazem Arafa, director of statistics.

“Companies are opening more oil and gas wells, with a rising share of new investment devoted to exploration and production of oil, both onshore and offshore,” he said. Overall investment in offshore production [has] increased from 6.5% of all domestic oil and gas production expenditures in 2011 to 7.1% in 2012, according to the survey.