Standard & Poor's Rates Penn Virginia 'BB-'

"The ratings on (Penn Virginia) reflect the (oil and gas exploration and production) industry's highly capital intensive and cyclical nature; Penn Virginia's limited scale and product diversity; and our view that U.S. natural gas prices are likely to remain weak in the near term," Standard & Poor's credit analyst David Lundberg said in a statement.

"The ratings also reflect Penn Virginia's competitive cost structure; relatively moderate financial leverage; and the benefit received from the dividends upstreamed from Penn Virginia Resources Partners," he added.

Shares of Penn Virginia fell 78 cents, or 3.7 percent, to $20.53 in after-hours trading. During the regular session the stock rose $1.21, or 6 percent, to close at $21.31.