Pioneer Natural Resources Co. (PXD) added 210 million barrels of oil equivalent (MMboe) of proved reserves during 2015 from discoveries, extensions and technical revisions of previous estimates, the company said on Feb. 10.

The continued success of the horizontal drilling program in the Spraberry/Wolfcamp and improved performance and reduced costs in the Spraberry/Wolfcamp, Raton and West Panhandle areas contributed to the addition of proved reserves.

Nymex prices in 2015 for the proved reserves were $50.11/bbl of oil and $2.59 per million British thermal units (MMBtu) of gas. The oil price for 2015 was 47% below 2014’s $94.98/bbl used to calculate proved reserves. The gas price for 2015 was 40% below 2014’s $4.35/MMBtu. This led to the negative price revisions of 269 MMBOE across all of Pioneer’s assets, the company said.

On Dec. 31, 2015, all of Pioneer’s proved reserves were in the U.S. and 89% were proved developed - 47% oil, 19% NGL and 34% gas.

Total costs incurred during 2015 were $2.2 billion, including $2 billion for exploration and development spending, $36 million for small bolt-on property acquisitions in the Spraberry/Wolfcamp area and $163 million for asset retirement obligations, capitalized interest and geological and geophysical costs.

In 2015, 136 MMbbl of proved developed reserves were added from discoveries and extensions and transfers from proved undeveloped reserves at year-end 2014.

Independent reserve engineering firm Netherland, Sewell & Associates Inc. audited the proved reserves of significant fields.

Pioneer Natural Resources Co. is based in Dallas.