Abstract:Recent droughts and concerns about water use for petroleum extraction renew the need to inventory water use for oil production. We quantified water volumes used and produced by conventional oil production and hydraulic fracturing (HF) in California. Despite a 25% decrease in conventional oil production from 1999 to 2012, total water use increased by 30% though much of that increase was derived from reuse of produced water. Produced water volumes increased by 50%, with increasing amounts disposed in unlined evaporation ponds or released to surface water. Overall freshwater use (constituting 1.2% of the state’s nonagricultural water consumption) increased by 46% during this period due to increased freshwater-intensive tertiary oil production. HF has been practiced in California for more than 30 years, accounting for 1% of total oil production in 2012 from mostly directional and vertical wells. Water use intensity for HF wells in California averaged at 3.5 vol water/vol oil production in 2012 and 2.4 vol/vol in 2013, higher than the range from literature estimates and net water use intensity of conventional production (1.2 vol/vol in 2012). Increasing water use and disposal for oil production have important implications for water management and have potentially adverse health, environmental, and ecological impacts.