13. Significant Concentrations

Major customers. Purchasers that accounted for more than 10% of the Company’s total sales for the periods presented are as follows:


	Year Ended December 31,
	2012			2011			2010
Musket Corporation		10	%		N/A			N/A
Texon L.P.		N/A			18	%		19	%
Plains All American Pipeline L.P.		N/A			16	%		28	%
Enserco Energy Inc.		N/A			15	%		N/A
Whiting Petroleum Corporation		N/A			N/A			11	%

N/A	Not applicable as the sales to these purchasers did not account for more than 10% of the Company’s total sales for such respective periods.

Total sales are related to the exploration and production segment, as OWS has exclusively provided well services to OPNA, and its external revenues relate to the other working interest owners in OPNA’s wells. No other purchasers accounted for more than 10% of the Company’s total sales for the years ended December 31, 2012, 2011 and 2010. Management believes that the loss of any of these purchasers would not have a material adverse effect on the Company’s operations, as there are a number of alternative oil and natural gas purchasers in the Company’s producing regions.

Substantially all of the Company’s accounts receivable result from sales of oil and natural gas as well as joint interest billings (“JIB”) to third-party companies who have working interest payment obligations in projects completed by the Company. No third-party company accounted for more than 10% of the Company’s total JIB receivables balance at December 31, 2012. Northern Oil & Gas Inc. and Hess Corporation accounted for approximately 16% and 14%, respectively, of the Company’s JIB receivables balance at December 31, 2011.

This concentration of customers and joint interest owners may impact the Company’s overall credit risk, either positively or negatively, in that these entities may be similarly affected by changes in economic or other conditions.