Additional Balance Sheet Detail

The following table summarizes components of selected balance sheet accounts as of the dates presented:



	As of December 31,
	2014		2013
Other current assets:
Tubular inventory and well materials	$	5,802	$	2,271
Prepaid expenses	4,215		3,653
Other	97		—
	$	10,114	$	5,924
Other assets:
Debt issuance costs	$	26,194	$	30,239
Assets of supplemental employee retirement plan ¹	4,123		3,734
Other	95		562
	$	30,412	$	34,535
Accounts payable and accrued liabilities:
Trade accounts payable	$	174,496	$	120,278
Drilling and other lease operating costs	68,842		51,529
Royalties	27,883		39,929
Compensation-related ^{2, 3, 4}	9,197		8,584
Interest	15,555		15,718
Preferred stock dividends	6,067		1,725
Other	10,187		10,241
	$	312,227	$	248,004
Other liabilities:
Deferred gains on sales of assets	$	90,569	$	—
Firm transportation obligation	12,042		13,245
Asset retirement obligations	5,889		6,437
Defined benefit pension obligations ²	1,753		1,579
Postretirement health care benefit obligations ²	890		1,023
Compensation-related ⁴	7,631		5,839
Deferred compensation - supplemental employee retirement plan obligation and other ¹	4,183		3,883
Other	929		1,380
	$	123,886	$	33,386

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¹ Includes the assets and liabilities of the Penn Virginia Corporation Supplemental Employee Retirement Plan (“SERP”) which is a nonqualified supplemental employee retirement savings plan. Assets of the SERP are held in a Rabbi Trust. Shares of our common stock held by the Rabbi Trust are presented for financial reporting purposes as treasury stock carried at cost.

² Includes the combined unfunded benefit obligations under our defined benefit pension and postretirement health care plans of $2.8 million and $3.0 million as of December 31, 2014 and 2013. The expense recognized with respect to these plans was $0.1 million, $0.3 million and $0.3 million for the years ended December 31, 2014, 2013 and 2012, respectively.

³ Includes employer matching obligations under our defined contribution retirement plan of $0.3 million and $0.2 million as of December 31, 2014 and 2013, respectively. The expense recognized with respect to this plan was $1.7 million, $1.0 million and $0.9 million for the years ended December 31, 2014, 2013 and 2012, respectively.

⁴ Includes liability-classified share-based compensation awards of $2.9 million representing amounts currently payable in cash in 2015 and $6.4 million and $4.8 million representing estimated amounts payable in cash based on valuations prepared as of December 31, 2014 and 2013, respectively.