NEW YORK (TheStreet) -- Gastar Exploration (GST) was falling 6.4% to $7.15 after-hours Monday after announcing a public offering of common stock.

The oil and gas company announced it will offer 17 million shares of common stock in the new public offering. The underwriters of the offering will have a 30-day option to buy an additional 2.55 million shares of common stock.

Gastar said it plans to part of the use the proceeds from the public offering to repay all the outstanding borrowings under its revolving credit facility. The company will use the remaining proceeds to fund its drilling and development program, and for general corporate purposes.

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In a separate announcement, Gastar said its board of directors approved a capital budget for 2015 of about $257.3 million.

GST data by YCharts

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