Note 6 - Warrants

6 Months Ended

Jun. 30, 2018

Notes to Financial Statements

Warrants [Text Block]

6. Warrants

At

June 30, 2018

and

December 31, 2017,

we had

4,863,158

and

6,688,849

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

$4.41

and

$4.50,

respectively. During the

three

and

six

month period ended

June 30, 2018,

1,813,691

and

1,825,691

warrants were exercised with a weighted average exercise price of

$4.75,

yielding proceeds of

$8.6

million and

$8.7

million, respectively. Subsequent to quarter end through

July 30, 2018,

an additional

274,798

warrants were exercised with a weighted average exercise price of

$4.75,

yielding

$1.3

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

March 2021

and

May 2021.