For the period ended June 30, the Texas-based company recorded a 15% increase in year-on-year quarterly revenues to a record $US91.4 million.

Coal royalty revenues were up 21% to another record, $69.8 million, while average coal royalty revenue per ton increased 23% over the same quarter last year to a record $6.05.

Net income attributable to its limited partners also went up 83% to a record $51.3 million. Half of the increase was attributable to increased revenues and $13 million was associated with the company’s elimination of incentive distribution rights last September.

"Central Appalachian quarterly production from our properties reached a level that we have not seen since the first quarter of 2009 and metallurgical coal for the six-month period accounted for 37% of coal production and an unprecedented 47% of NRP's coal royalty revenues," president Nick Carter said.

It was spending money at the same time, the company pointed out, but that expenditure was related to NRP’s future growth.

“Most of the investment was related to the Deer Run mine in the Illinois Basin, where we acquired additional reserves for $70 million,” NRP said.

“The remaining $30 million was used to acquire three previously announced aggregate properties.”

NRP expects that the Deer Run purchase should significantly increase coal production from the Illinois Basin next year.

Looking ahead, the MLP said in its guidance that coal royalty revenues initially ranged between $235 and $270 million will now be between $255 and $270 million.

Coal production, which was estimated at 42 to 52 million tons, is now anticipated to be between 42 and 50Mt.

“NRP is narrowing the ranges and modestly increasing the midpoint of its guidance for the remainder of the year due to the record revenues experienced in the first half of 2011,” the company explained.

Carter noted that, although the company benefitted from its significant met coal exposure in the first half of the year, about 13% of our metallurgical revenues came from the Pinnacle and Oak Grove mines – both of which have since been plagued by issues.

"The Oak Grove mine in Alabama suffered damage to its preparation plant due to a tornado, and is not expected to sell any coal in the third quarter,” he said.

“The Pinnacle mine in West Virginia has experienced a high level of carbon monoxide and remains closed until MSHA determines that the mine is safe. As a result, we expect to receive a lower percentage of revenues from metallurgical coal sales in the second half of the year."