Lease operating expenses, before severance and ad valorem taxes, were $9.70 per Boe in the fourth quarter 2012, a decrease of 1% compared to $9.82 per Boe in the fourth quarter of 2011. Aggregate lease operating expenses increased 14% due to higher gas processing, chemical treating costs and lease supervision costs from our South Texas operations, associated with higher production volumes in the current period.
Severance and ad valorem taxes decreased to $4.19 per Boe in the fourth quarter 2012 from $4.92 per Boe in the fourth quarter of 2011 due to a higher percentage of production in Texas, as Texas has a lower severance tax rate for oil than Louisiana.
General and administrative expenses decreased to $3.46 per Boe during the fourth quarter of 2012 from $4.70 per Boe in the same period in 2011, again due to higher production volumes in the current quarter. Interest expense increased to $5.39 per Boe in the fourth quarter of 2012 compared to $3.75 per Boe for the same period in 2011 due primarily to the additional $150 million of long-term debt that was issued during the fourth quarter 2012.
Reserve EstimatesSwift Energy’s year-end 2012 estimate of proved reserves as of December 31, 2012 was 192.1 MMBoe, 20% higher than 2011 year-end proved reserves of 159.6 MMBoe. These year-end 2012 proved reserves are 48% crude oil and natural gas liquids and 34% proved developed. Swift Energy’s year-end 2012 proved reserves were valued at approximately $2.3 billion of present value discounted at 10% per year (PV-10), compared to a PV-10 value of $1.9 billion for the Company’s 2011 year-end proved reserves, a 19% increase despite lower gas prices. Pricing for 2012 reserves and PV-10 calculations utilized $103.64 per barrel for crude oil and $2.71 per thousand cubic feet (“Mcf”) for natural gas, compared to $103.87 per barrel and $3.89 per Mcfe used for reserves valuation at year-end 2011. (See page 7 for a reconciliation of PV-10 value at year-end 2012, a non-GAAP measure, to the GAAP standardized measure of discounted future cash flows).