percent from 2013. Net natural gas production averaged about 1.3 billion cubic feet per day in 2015, up 5 percent from 2014 and 2013. Refer to the “Selected Operating Data” table on page FS-11 for a three-year comparison of production volumes in the United States.

International Upstream

International upstream earnings were $2.09 billion in 2015 compared with $13.57 billion in 2014. The decrease between periods was primarily due to lower crude oil and natural gas realizations of $10.57 billion and $880 million, respectively, and higher depreciation expenses of $1.11 billion, primarily reflecting impairments. Lower gains on asset sales also contributed to the decrease with current year gains of $370 million compared with $1.10 billion in 2014. Partially offsetting the decrease were higher crude oil sales volumes of $590 million and lower operating expenses of $510 million. Foreign currency effects increased earnings by $725 million in 2015, compared with an increase of $597 million a year earlier.

International upstream earnings were $13.57 billion in 2014 compared with $16.77 billion in 2013. The decrease between periods was primarily due to lower crude oil prices and sales volumes of $1.97 billion and $400 million, respectively. Also contributing to the decrease were higher depreciation expenses of $1.02 billion, mainly related to impairments and other asset write-offs, and higher operating and tax expenses of $340 million and $310 million, respectively. Partially offsetting these items were gains on asset sales of $1.10 billion in 2014, compared with $140 million in 2013. Foreign currency effects increased earnings by $597 million in 2014, compared with a decrease of $559 million a year earlier.

The company’s average realization for international crude oil and natural gas liquids in 2015 was $46.52 per barrel, compared with $90.42 in 2014 and $100.26 in 2013. The average natural gas realization was $4.53 per thousand cubic feet in 2015, compared with $5.78 and $5.91 in 2014 and 2013, respectively.

International net oil-equivalent production was 1.90 million barrels per day in 2015, essentially unchanged from 2014 and down 2 percent from 2013. Between 2015 and 2014, production increases from entitlement effects in several locations and project ramp-ups in Bangladesh and other areas were offset by the Partitioned Zone shut-in, normal field declines and the effect of asset sales. Between 2014 and 2013, production increases due to project ramp-ups in Nigeria, Argentina and Brazil were more than offset by normal field declines, production entitlement effects in several locations and the effect of asset sales.

The net liquids component of international oil-equivalent production was 1.24 million barrels per day in 2015, a decrease of approximately 1 percent from 2014 and a decrease of approximately 3 percent from 2013. International net natural gas production of 4.0 billion cubic feet per day in 2015 was up 1 percent from 2014 and unchanged from 2013.

Refer to the “Selected Operating Data” table, on page FS-11, for a three-year comparison of international production volumes.

U.S. Downstream

U.S. downstream operations earned $3.18 billion