NATURAL GAS SERVICES GROUP

Ticker: NGS CUSIP: 63886Q109 Class: Common Stock

Parallax Volatility Advisers, L.P.'s Holding History (CIK: 0001521001)

Note: Option positions (PUT/CALL) are excluded.

Q4 2017

Shares 1,974 Value ($000) $52 Avg Close $26.38 Range $23.89 - $29.04

Q1 2014

Shares 651 Value ($000) $20 Avg Close $29.49 Range $25.23 - $34.59

Q4 2013

Shares 1,590 Value ($000) $44 Avg Close $27.72 Range $24.44 - $30.62

Period	Shares	Value ($000)	Average Close	Price Range
Q4 2017	1,974	$52	$26.38	$23.89 - $29.04
Q1 2014	651	$20	$29.49	$25.23 - $34.59
Q4 2013	1,590	$44	$27.72	$24.44 - $30.62