We have two active equity-based stock plans, our Amended and Restated 2005 Equity-Based Compensation Plan, which we refer to as the 2005 Plan and the Amended and Restated 2019 Equity-Based Compensation Plan, which was approved by our stockholders in May 2019 and amended in May 2020. Under these plans, the Compensation Committee of the board of directors may grant, various awards to non-employee directors and employees. Shares issued as a result of awards granted are generally new common shares but can be funded out of treasury shares, if available.

Stock-based compensation expense represents amortization of restricted stock and performance units. The following table details the amount of stock-based compensation that is allocated to functional expense categories for each of the years in the three-year period ended December 31, 2020 (in thousands):

	2020		2019			2018
Direct operating expense	$	1,078		$	1,928		$	2,109
Brokered natural gas and marketing expense		1,416			1,856			1,452
Exploration expense		1,279			1,566			1,921
General and administrative expense		32,905			35,061			43,806
Termination costs		2,165			1,971			—
Total stock-based compensation	$	38,843		$	42,382		$	49,288

Unlike the other forms of stock-based compensation expense mentioned above, the mark-to-market of the liability related to the vested restricted stock held in our deferred compensation plans is directly tied to the change in our stock price and not directly related to the functional expenses. Therefore, the liability related to the vested restricted stock held in our deferred compensation plans is not allocated to the functional categories and is reported as deferred compensation plan expense in the accompanying consolidated statements of operations.

In 2020, we recorded $4.3 million additional tax expense for the tax effect of excess financial accounting expense over the corporate income tax deduction for equity compensation vested in the year compared to $3.4 million in 2019 and $3.6 million in 2018.

Restricted Stock Awards. We grant restricted stock units under our equity-based stock compensation plans. These restricted stock units, which we refer to as restricted stock Equity Awards, generally vest over a three-year period and are contingent on the recipient’s continued employment. These awards are net settled by withholding shares to satisfy income tax withholding payments due upon vesting. The remaining shares are remitted to individual brokerage accounts. The grant date fair value of the Equity Awards is based on the fair market value of our common stock on the date of grant. Shares to be delivered upon vesting are made available from authorized but unissued shares or shares held as treasury stock.

The compensation committee also grants restricted stock to certain employees and non-employee directors of the board of directors as part of their compensation. We also grant restricted stock to certain employees for retention purposes. Compensation expense is recognized over the balance of the vesting period, which is typically three years for employee grants and immediate vesting for non-employee directors. In May 2020, vesting for non-employee directors was changed to one year after grant date. All restricted stock awards are issued at prevailing market prices at the time of the grant and the vesting is based upon an employee’s continued employment with us. Prior to vesting, all restricted stock awards have the right to vote such stock (by the trustee) and receive dividends thereon. Upon grant of these restricted shares, which we refer to as restricted stock Liability Awards, the majority of these shares are generally placed in our deferred compensation plan and, upon vesting, withdrawals are allowed in either cash or in stock. These Liability Awards are classified as a liability and are remeasured at fair value each reporting period. This mark-to-market amount is reported in deferred compensation plan expense in the accompanying consolidated statements of operations. Historically, we have used authorized but unissued shares of stock when restricted stock is granted. However, we also may utilize treasury shares when available.

Stock-Based Performance Units. We grant three types of performance share awards: two of which are based on performance conditions measured against internal performance metrics (Production Growth Awards or “PG-PSUs” and Reserve Growth Awards or “RG-PSUs”) and one based on market conditions measured based on Range’s performance relative to a predetermined peer group (“TSR Award” or “TSR-PSUs”).

At grant date, each unit represents the value of one share of our common stock. These units are settled in stock and the amount of the payout is based on (1) the vesting percentage, which can be from zero to 200% based on the performance achieved and (2) the value of our common stock on the date payout is determined by the compensation committee. Dividend equivalents may accrue during the performance period and would be paid in stock at the end of the performance period. The performance period for TSR-PSUs is three years. The performance period for the PG-PSUs and RG-PSUs is based on annual performance targets earned over a three-year period.

In 2020, we granted 4.5 million restricted stock Equity Awards to employees which generally vest over a three-year period compared to 2.8 million in 2019 and 1.8 million in 2018. We recorded compensation expense for these awards of $17.8 million in the year ended December 31, 2020 compared to $22.5 million in 2019 and $24.2 million in 2018. As of December 31, 2020, there was $15.1 million of unrecognized compensation related to Equity Awards expected to be recognized over a weighted average period of 1.6 years. Restricted stock Equity Awards are not issued to employees until such time as they are vested and the employees do not have the option to receive cash.

In 2020, we granted 3.5 million shares of restricted stock Liability Awards as compensation to directors and employees at an average price of $3.18. These grants included 217,000 shares issued to non-employee directors, which vest at the end of one year, and 3.3 million shares to employees with vesting generally over a three-year period. In 2019, we granted 1.2 million shares of restricted stock Liability Awards as compensation to directors and employees at an average price of $10.16. This grant included 183,000 shares issued to non-employee directors, which vested immediately, and 1.0 million shares to employees with vesting generally over a three-year period. In 2018, we granted 891,000 shares of restricted stock Liability Awards as compensation to directors and employees at an average price of $15.30. These grants included 146,000 shares issued to non-employee directors, which vested immediately, and 745,000 shares to employees with vesting generally over a three-year period. We recorded compensation expense for these restricted stock Liability Awards of $10.3 million in the year ended December 31, 2020 compared to $9.3 million in 2019 and $11.7 million in 2018. As of December 31, 2020, there was $4.2 million of unrecognized compensation related to restricted stock Liability Awards expected to be recognized over a weighted average period of 1.4 years. A large portion of these awards are held in our deferred compensation plan, are classified as a liability and are remeasured at fair value each reporting period. This mark-to-market amount is reported as deferred compensation expense in our consolidated statements of operations (see additional discussion below). The proceeds received from the sale of stock held in our deferred compensation plan were $696,000 in 2020 compared to $667,000 in 2019 and $9.7 million in 2018. The following is a summary of the status of our non-vested restricted stock outstanding at December 31, 2020:

	Restricted Stock Equity Awards					Restricted Stock Liability Awards
	Shares			Weighted Average Grant Date Fair Value		Shares			Weighted Average Grant Date Fair Value
Outstanding at December 31, 2019		2,002,239		$	12.32		411,126		$	10.94
Granted		4,462,711			3.42		3,535,093			3.18
Vested		(3,063,652	)		6.93		(2,678,013	)		3.94
Forfeited		(585,438	)		8.03		(81,570	)		3.02
Outstanding at December 31, 2020		2,815,860		$	4.97		1,186,636		$	4.18

Production Growth and Reserve Growth Awards. The PG-PSUs and RG-PSUs vest at the end of the three-year performance period. The performance metrics for each year are set by the compensation committee no later than March 31 of such year. If the performance metric for the applicable period is not met, then that portion is considered forfeited. The following is a summary of our non-vested PG/RG-PSUs award activities at December 31, 2020:


	Number of Units			Weighted Average Grant Date Fair Value
Outstanding at December 31, 2019	881,573		$	11.70
Units granted ^(a)	777,847			2.33
Vested	(101,150	)		15.32
Forfeited ⁽^b⁾	(459,168	)		2.33
Outstanding at December 31, 2020	1,099,102		$	5.92

^(a) Amounts granted reflect the number of performance units granted; however, the actual payout of shares will be between zero and 200% depending on achievement of specifically identified performance targets.

⁽^b⁾For RG-PSU’s tranches granted in 2018, 2019 and 2020 which are set to vest in early 2021, the performance metric is not expected to be met and are considered forfeited. For PG-PSU’s tranches granted in 2018, 2019 and 2020 which are set to vest in early 2021, the payout is estimated at 23% with the remainder considered to be forfeited.

We recorded PG/RG-RSUs compensation expense of $2.7 million in the year ended December 31, 2020 compared to $3.8 million in the year ended December 31, 2019 and $5.4 million in the year ended December 31, 2018. As of December 31, 2020, there was $768,000 of unrecognized compensation related these PSU awards to be recognized over a weighted average period of 1.0 years.

TSR Awards. TSR-PSUs granted are earned, or not earned, based on the comparative performance of Range’s common stock measured against a predetermined group of companies in the peer group over a three-year performance period. The fair value of the TSR-PSUs is estimated on the date of grant using a Monte Carlo simulation model which utilizes multiple input variables that determine the probability of satisfying the market condition stipulated in the award grant and calculates the fair value of the award. The fair value is recognized as stock-based compensation expense over the three-year performance period. Expected volatilities utilized in the model were estimated using a combination of a historical period consistent with the remaining performance period of three years and option implied volatilities. The risk-free interest rate was based on the United States Treasury rate for a term commensurate with the life of the grant. The following assumptions were used to estimate the fair value of the TSR-PSUs granted during the years ended December 31, 2020, 2019 and 2018:

	Year Ended December 31, 2019
	2020			2019			2018
Risk-free interest rate		1.4	%		2.44	%		2.42	%
Expected annual volatility		65	%		46	%		48	%
Grant date fair value per unit	$	3.85		$	11.34		$	18.51

	Number of Units			Weighted Average Grant Date Fair Value
Outstanding at December 31, 2019		993,452		$	19.00
Granted ^(a)		610,155			3.85
Vested and issued ⁽^b⁾		(278,184	)		26.12
Forfeited		(75,899	)		26.66
Outstanding at December 31, 2020		1,249,524		$	9.55

^(a) These amounts reflect the number of performance units granted. The actual payout of shares may be between zero and 200% of the performance units granted depending on the total shareholder return ranking compared to our peer companies at the vesting date.

⁽^b⁾ Includes 278,184 TSR-PSUs awards issued related to 2017 performance where the return on our common stock was in the 60^th percentile for the March 2017 grant and the 80^th percentile for the May 2017 grant. The remaining 2017 awards were considered to be forfeited.

We recorded TSR-PSU compensation expense of $2.4 million in the year ended December 31, 2020 compared to $3.0 million in the year ended December 31, 2019 and $6.3 million in the year ended December 31, 2018. As of December 31, 2020, there was $1.3 million of unrecognized compensation related to these PSU awards to be recognized over a weighted average period of 1.7 years.

We maintain a 401(k) benefit plan that allows employees to contribute up to 75% of their salary (subject to Internal Revenue Service limitations) on a pretax basis. We match up to 6% of salary in cash and vesting of those contributions is immediate. In 2020, we contributed $5.3 million to the 401(k) Plan compared to $5.4 million in 2019 and $5.8 million in 2018. Employees have a variety of investment options in the 401(k) benefit plan.

Our deferred compensation plan gives directors, officers and key employees the ability to defer all or a portion of their salaries and bonuses and invest in Range common stock or make other investments at the individual’s discretion. Range provides a partial matching contribution which vests over three years. The assets of the plans are held in a grantor trust, which we refer to as the Rabbi Trust, and are therefore available to satisfy the claims of our creditors in the event of bankruptcy or insolvency. Our stock held in the Rabbi Trust is treated as a liability award as employees are allowed to take withdrawals from the Rabbi Trust either in cash or in Range stock. The liability for the vested portion of the stock held in the Rabbi Trust is reflected in the deferred compensation liability in the accompanying consolidated balance sheets and is adjusted to fair value each reporting period by a charge or credit to deferred compensation plan expense on our consolidated statements of operations. The assets of the Rabbi Trust, other than our common stock, are invested in marketable securities and reported at their market value in other assets in the accompanying consolidated balance sheets. The deferred compensation liability reflects the vested market value of the marketable securities and Range stock held in the Rabbi Trust. Changes in the market value of the marketable securities and changes in the fair value of the deferred compensation plan liability are charged or credited to deferred compensation plan expense each quarter. We recorded mark-to-market loss of $12.5 million in 2020 compared to a gain of $15.5 million in 2019 and a gain of $18.6 million in 2018. The Rabbi Trust held 6.1 million shares (5.0 million of vested shares) of Range stock at December 31, 2020 compared to 3.2 million (2.7 million of vested shares) at December 31, 2019.

We have a post retirement benefit plan to assist in providing health care to officers who are active employees (including their spouses) and have met certain age and service requirements. These benefits are not funded in advance and are provided up to age 65 or on the date they become eligible for Medicare, subject to various cost-sharing features. The change in our post-retirement benefit obligation is as follows (in thousands):

Change in Benefit Obligation:	2020			2019
Benefit obligation at beginning of year	$	1,957		$	1,355
Service cost		80			88
Interest cost		50			68
Actuarial (gain) loss		(39	)		532
Benefits paid		(95	)		(86	)
Benefit obligation at end of year	$	1,953		$	1,957

Amounts recognized in the consolidated balance sheet:
Long-term liabilities	$	1,953		$	1,957

Components of Net Periodic Post Retirement Benefit Cost:
Service cost	$	80		$	88
Interest cost		50			68
Amortization of prior service cost		369			369
Net periodic post retirement costs (recognized in general and administrative expense)	$	499		$	525

Other Changes in Benefit Obligations in Other Comprehensive Income (Loss):
Net (gain) loss	$	(39	)	$	532
Prior service cost		—			—
Amortization of prior service cost		(369	)		(369	)
Total recognized in other comprehensive (loss) income	$	(408	)	$	163
Total recognized in net periodic benefit cost and other comprehensive income	$	91		$	688

The following summarizes the assumptions used to determine the benefit obligation at December 31, 2020 and 2019:

	December 31, 2020			December 31, 2019
Weighted average assumptions used to determine benefit obligation:
Discount rate		1.9	%		2.9	%
Assumed weighted average healthcare cost trend rates:
Initial healthcare trend rate		6.5	%		6.5	%
Ultimate trend rate		4.5	%		4.5	%
Year ultimate trend rate reached		2024			2023

The expected future benefit payments under our post-retirement benefit plan for the next ten years is $914,000 for the five year period 2021 through 2025 and $371,000 for the five year period 2026 through 2030. The estimated prior service cost that will be amortized from accumulated other comprehensive loss into our statements of operations in 2021 is $369,000.