Note 6 - Warrants

9 Months Ended

Sep. 30, 2018

Notes to Financial Statements

Warrants [Text Block]

6. Warrants

At

September 30, 2018

and

December 31, 2017,

we had

4,306,005

and

6,688,849

warrants outstanding, respectively, and exercisable with a weighted average exercise price of

$4.37

and

$4.50,

respectively. During the

three

and

nine

month period ended

September 30, 2018,

557,153

and

2,382,844

warrants were exercised with a weighted average exercise price of

$4.75

,

yielding proceeds of

$2.6

million and

$11.3

million, respectively. Subsequent to quarter end through

November 7, 2018,

an additional

225,000

warrants were exercised with a weighted average exercise price of

$4.75,

yielding

$1.1

million in proceeds to the Company. The outstanding warrants have expiration dates between

March 2021

and

May 2021.