total reserve additions, 156 percent, or about 433 million barrels, resulted from our development program.
"Our focus on capital and operating efficiencies helped us generate $12.9 billion of cash flow from operations during the twelve months of 2013. We spent $8.8 billion of our cash flow on capital expenditures, repurchased almost 11 million shares and reduced our debt by 9 percent. Our year-end cash balance was $3.4 billion compared to the 2012 year-end level of $1.6 billion."
TWELVE-MONTH RESULTS
Oil and Gas
Oil and gas core earnings were $8.5 billion for the twelve months of 2013, compared with $8.8 billion for the same period of 2012. The 2013 results reflect higher domestic earnings resulting from improved oil and gas realized prices and higher liquids volumes, lower operating costs partially offset by higher DD&A rates and lower NGL prices. International results were lower on a year-over-year basis, due to lower liquids sales volumes, lower oil prices and higher operating costs and DD&A rates in the Middle East/North Africa.
Operating costs dropped significantly in 2013 compared with 2012. Domestic operating costs for the twelve months of 2013 were $14.43 per barrel, compared to $17.43 for the full year of 2012. For the entire company, operating costs for the twelve months were $13.76 per barrel, compared to $14.99 for the full year of 2012.
Oil and gas production volumes for the twelve months were 763,000 barrels of oil equivalent per day (BOE) per day for 2013, compared with 766,000 BOE per day for the 2012 period. Year-over-year, Oxy’s domestic production increased by 9,000 BOE per day. International production was 12,000 BOE per day lower, mainly due to lower cost recovery barrels in the Dolphin and Oman operations and field and port strikes in Libya. Daily sales volumes were 762,000 BOE in the twelve months of 2013, compared with 764,000 BOE for 2012.
Oxy's worldwide realized prices were flat for crude oil and lower for NGLs but increased for both domestic crude oil and natural gas on a year-over-year basis. Worldwide realized crude oil prices were $99.84 per barrel for the twelve months of 2013, compared with $99.87 per barrel for the twelve months of 2012. Worldwide NGL prices were $41.03 per barrel for the twelve months of 2013, a reduction of 9 percent from $45.18 per barrel for the twelve months of 2012. Domestic crude oil prices increased from $93.72 per barrel in the twelve months of 2012 to $96.42 per barrel in the twelve months of 2013. Domestic gas prices increased by about 29 percent from $2.62 per MCF in the twelve months of 2012 to $3.37 per MCF in the twelve months of 2013.
Chemical
Chemical core earnings were $612 million for the twelve months of 2013, compared with $720 million for the same period in 2012. The lower 2013 earnings primarily resulted from higher energy costs, higher ethylene costs and lower chlor-alkali and chlorinated organics