6. Warrant Liabilities

Liabilities measured at fair value on a recurring basis include warrant liabilities resulting from the Company’s past equity financings. In accordance with ASC 815-40, Derivatives and Hedging – Contracts in Entity’s Own Equity (“ASC 815-40”), the warrant liabilities are being recorded at fair value until they are completely settled. The warrants are valued using the Black-Scholes method, using assumptions consistent with the Company’s application of ASC 505-50, Equity-Based Payments to Non-Employees (“ASC 505-50”). The gain or loss resulting from the change in fair value is shown on the Condensed Statements of Operations as gain (loss) on warrant derivative liability. The Company recognized a gain (loss) of $2.4 million and ($2.5) million for the three-month periods ended June 30, 2015 and 2014, respectively, and a gain of $0.6 million and $12.2 million for the six-month periods ended June 30, 2015 and 2014, respectively. The following reflects the weighted-average assumptions for each of the six-month periods indicated:

	Six Months Ended June 30,
	2015			2014

Risk-free interest rate		0.28	%		0.44	%
Expected dividend yield		0	%		0	%
Expected lives		1.09			1.96
Expected volatility		62.7	%		84.1	%
Warrants classified as liabilities (in shares)		6,371,854			6,984,716

The Company’s computation of expected volatility is based on the historical daily volatility of its publicly traded stock. The dividend yield assumption of zero is based upon the fact that the Company has never paid cash dividends and presently has no intention to do so. The risk-free interest rate used for each warrant classified as a derivative is equal to the U.S. Treasury rates in effect at June 30 of each year presented. The expected lives are based on the remaining contractual lives of the related warrants at the valuation date.