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



	As of December 31,
	2013		2012
Other current assets:
Tubular inventory and well materials	$	2,271	$	4,033
Prepaid expenses	3,653		562
	$	5,924	$	4,595
Other assets:
Debt issuance costs	$	30,239	$	13,186
Assets of supplemental employee retirement plan ¹	3,734		3,237
Other	562		1,511
	$	34,535	$	17,934
Accounts payable and accrued liabilities:
Trade accounts payable	$	120,278	$	37,835
Drilling and other lease operating costs	51,529		37,703
Royalties	39,929		14,390
Production and franchise taxes	5,338		2,874
Compensation - related ^{2, 3}	8,584		6,853
Interest	15,718		5,828
Preferred stock dividends	1,725		1,687
Other	4,903		4,485
	$	248,004	$	111,655
Other liabilities:
Firm transportation obligation	$	13,245	$	14,333
Asset retirement obligations	6,437		4,513
Defined benefit pension obligations ²	1,579		1,821
Postretirement health care benefit obligations ²	1,023		2,634
Deferred compensation - supplemental employee retirement plan obligation and other ¹	3,883		3,310
Other	7,219		2,290
	$	33,386	$	28,901

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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 $3.0 million and $5.1 million as of December 31, 2013 and 2012. The expense recognized with respect to these plans was $0.3 million, $0.3 million and $0.4 million for the years ended December 31, 2013, 2012 and 2011, respectively.

³ Includes employer matching obligations under our defined contribution retirement plan of $0.2 million and $0.2 million as of December 31, 2013 and 2012, respectively. The expense recognized with respect to this plan was $1.0 million, $0.9 million and $1.2 million for the years ended December 31, 2013, 2012 and 2011, respectively.