Schedule of Warrants Issued to Entities Affiliated with Natural Gas Partners

This document lists warrants issued by the company to Natural Gas Partners VIII, L.P. and Energy Technology Partners, L.L.C. The warrants allow these entities to purchase specified numbers of common stock shares at an exercise price of $9.50 per share. The warrants were issued on August 1, 2006, and December 22, 2006, with expiration dates in 2014. The schedule details the number of shares, type of shares, exercise price, and expiration date for each warrant issued.