8. Warrant Liabilities

Liabilities measured at fair value on a recurring basis include warrant liabilities resulting from our equity financings. In accordance with ASC 815-40, Derivatives and Hedging – Contracts in Entity's Own Equity ("ASC 815-40"), the warrant liabilities are recorded at fair value until they are completely settled. The warrants are valued using the Black-Scholes method. 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. We recognized a gain of $0.2 million and $3.5 million for the three-month periods ended September 30, 2016 and 2015, respectively, and a gain of $0.9 million and $4.1 million for the nine-month periods ended September 30, 2016 and 2015, respectively. The following reflects the weighted-average assumptions for each of the nine-month periods indicated:

	Nine Months Ended September 30,
	2016			2015

Risk-free interest rate		0.52	%		0.21	%
Expected dividend yield		0	%		0	%
Expected lives		0.8			0.84
Expected volatility		131.3	%		69.1	%
Warrants classified as liabilities (in shares)		28,571,429			6,371,854

Our 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 we have never paid cash dividends and presently have 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 September 30 of each year presented. The expected lives are based on the remaining contractual lives of the related warrants at the valuation date.

On August 1, 2016, 6,371,854 warrants expired. On July 20, 2016, we issued one-year warrants to purchase up to 28,571,429 shares of our common stock in the public offering described in Note 12.