Exploration expense from continuing operations for the first quarter of 2013 was $2 million, unchanged from the first quarter of last year. First quarter 2013 exploration expenses were primarily associated with reservoir studies and exploration general and administrative expenses in the Utica Shale, whereas in the first quarter of 2012, costs were primarily associated with PDC Mountaineer's ("PDCM") geological and seismic testing of the Marcellus Shale, and PDCM's lease prospecting costs.
General and administrative expense from continuing operations for the first quarter of 2013 remained flat at $15 million compared to slightly under $15 million for the first quarter of 2012. First quarter 2013 expenses were primarily attributable to an increase in payroll and employee benefits, offset partially by a decrease in professional, consulting and legal costs.
Depreciation, depletion and amortization ("DD&A") expense related only to crude oil and natural gas properties from continuing operations was $27 million, or $16.06 per Boe, in the first quarter of 2013, compared to $27 million, or $18.89 per Boe, in the first quarter of last year. Per unit DD&A expense in 2013 decreased due to a lower weighted-average DD&A rate.
Interest expense for the first quarter of 2013 was $13 million, compared to $10 million for the first quarter of 2012. The $3 million increase was related to an increase in interest expense resulting from the issuance in October 2012 of $500 million 7.75% Senior Notes due 2022 which replaced $203 million 12% Senior Notes due in 2018, partially offset by lower average borrowings on PDC's credit facility during the first quarter of 2013 as compared to the first quarter of last year.The Company's available liquidity position as of March 31, 2013 was $388 million, compared to $308 million as of March 31, 2012. As of March 31, 2013, PDC had a balance of $57 million and an undrawn letter of credit of $19 million outstanding on its $450 million revolving credit facility. The Company's borrowing base is $450 million as of March 31, 2013 and is currently under customary semi-annual review for redetermination. No change in the borrowing base is expected as a result of the redetermination.