On April 29, 2011 the Board, upon the recommendation of the Remuneration Committee, adopted the 2011 Stock Incentive Plan, or 2011 Plan, which was approved by the Company’s shareholders on July 12, 2011. The 2011 Plan replaced the Company’s 2002 Stock Option Plan, or 2002 Plan, which expired on January 1, 2012. The maximum number of the Company’s Ordinary Shares of £0.50 each or any ADS’s, as to be issued under the 2011 Plan, as amended, shall not exceed the sum of (i) 51.5 million newly authorized Shares available for award and (ii) the number of Shares that remained available for grants under the Company’s 2002 Plan and (iii) the number of Shares underlying then outstanding awards under the 2002 Plan that could be subsequently forfeited, cancelled, expire or are otherwise terminated. The award of stock options (both incentive and non-qualified options) and restricted stock units, and awards of unrestricted Shares to Directors are permitted. The 2011 Plan is administered by the Remuneration Committee of the Company’s Board of Directors and expires on July 12, 2021.

In addition to the grants under the 2011 Plan, the Company grants non-qualified stock options to employees to purchase the Company’s ordinary shares. These grants are made pursuant to employment agreements on terms consistent with the 2011 Plan.

Under the terms of the 2011 Plan, and grants made pursuant to employment agreements, options typically vest over a four-year period, expire after a ten-year term and are granted at an exercise price equal to the closing price of the Company’s American Depositary Shares on the grant date. The following table summarizes all stock option activity for the year ended December 31, 2019:

In thousands (except per share amounts and years)	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term	Aggregate Intrinsic Value
Outstanding as of January 1, 2019		19,263		$	4.29
Granted		2,648			17.07
Forfeited		(291	)		10.31
Expired		(3	)		4.04
Exercised		(5,998	)		4.09
Outstanding as of December 31, 2019		15,619			6.43	6.5 years	$	234,499
Exercisable as of December 31, 2019		10,310			3.75	5.4 years		182,417
Vested and expected to vest as of December 31, 2019		15,354		$	6.34	6.4 years	$	231,895
Available for future grant as of December 31, 2019		7,851

The weighted average grant date fair value of stock options granted during the years ended December 31, 2019, 2018, and 2017 was $17.07, $7.82, and $3.09, respectively. The total grant date fair value of options vested during the years ended December 31, 2019, 2018, and 2017 was $14.5 million, $7.7 million, and $7.1 million, respectively.

During the years ended December 31, 2019, 2018 and 2017, the Company received proceeds from the exercise of options of $24.5 million, $26.4 million, and $0.6 million, respectively. The total intrinsic value of options exercised during the years ended December 31, 2019, 2018, and 2017 was $90.5 million, $69.7 million, and $0.5 million, respectively, calculated as the difference between the quoted stock price of the Company’s common stock as of the reporting date and the exercise prices of the underlying awards.

As of December 31, 2019, there was $40.5 million of unrecognized stock-based compensation expense related to unvested stock option share-based compensation arrangements granted under the Company’s stock award plans. This expense is expected to be recognized over a weighted-average period of approximately 2.6 years. The Company recognizes compensation expense for the fair values of those awards which have graded vesting on a straight-line basis.

The fair value of stock options on the date of grant was estimated using the Black-Scholes option pricing model. Use of a valuation model requires management to make certain assumptions with respect to selected model inputs. Expected stock price volatility was calculated based on the historical volatility of the Company’s common stock over the expected life of the option. The expected life was determined using the simplified method based on the term and vesting period. The risk-free interest rate is based on zero-coupon U.S. Treasury securities with a maturity term approximating the expected life of the option at the date of grant. No dividend yield has been assumed as the Company does not currently pay dividends on its common stock and does not anticipate doing so in the foreseeable future. Estimated forfeitures are based on the Company’s historical forfeiture activity.

Employee stock options generally vest over a four-year service period and all stock options are settled by the issuance of new shares. Compensation expense recognized for all option grants is net of estimated forfeitures and is recognized over the awards’ respective requisite service periods. The vesting of certain stock options is contingent upon the attainment of performance criteria. The probability that such criteria will be achieved is assessed by management and compensation expense for such awards is only recorded to the extent that the attainment of the performance criteria is deemed to be probable. The Company recorded compensation expense in relation to stock options of $16.3 million, $8.2 million, and $7.0 million for the years ended December 31, 2019, 2018, and 2017, respectively.

For 2019, 2018, and 2017, the Company used the following assumptions to estimate the fair value of share-based payment awards:

	2019	2018	2017
Risk-free interest rate	1.55% - 2.95%	2.18% - 3.00%	1.77% - 2.01%
Expected dividend yield	0.00%	0.00%	0.00%
Expected option life (years)	6.25	6.25	6.25
Expected volatility	92% - 94%	71% - 92%	73% - 82%

The 2011 Plan also allows for granting of restricted stock unit awards under the terms of the Plan. The restricted stock units vest based upon a time-based service condition, a performance condition, or both. The probability that any performance criteria will be achieved is assessed by management and compensation expense for such awards is only recorded to the extent that the attainment of the performance criteria is deemed to be probable. Restricted stock units are recorded as compensation expense based on fair value, representing the market value of the Company’s common stock on the date of grant. The fair value of restricted stock units is amortized on a straight-line basis through the statement of operations over the service period until the shares have vested. The following table presents the restricted stock unit activity for the years ended December 31, 2019 and 2018:

In thousands (except per share amounts)	Shares			Weighted Average Grant Date Fair Value
Outstanding as of January 1, 2018		12,006		$	2.50
Granted		2,633			4.32
Vested		(4,611	)		2.20
Forfeited		(395	)		3.43
Outstanding as of December 31, 2018		9,633			3.12
Granted		1,473			16.83
Vested		(3,970	)		2.56
Forfeited		(215	)		3.25
Outstanding as of December 31, 2019		6,921		$	6.34

The Company recorded compensation expense in relation to restricted stock units of $14.6 million, $10.6 million, and $7.0 million for the years ended December 31, 2019, 2018, and 2017 respectively.

The following table presents the stock-based compensation expense related to stock-based awards for the years ended December 31, 2019, 2018, and 2017:

In thousands	2019		2018		2017
Research and development	$	4,615	$	2,898	$	2,122
Selling, general and administrative		26,302		15,908		11,838
Stock-based compensation expense	$	30,917	$	18,806	$	13,960

On March 13, 2017, the Board adopted, subject to shareholder approval, the Amarin Corporation plc 2017 Employee Stock Purchase Plan, or the ESPP, which was approved by the Company’s shareholders on May 15, 2017. The ESPP is intended to qualify as an “employee stock purchase plan” within the meaning of Section 423 of the Internal Revenue Code. The maximum fair market value of stock which can be purchased by a participant in a calendar year is $25,000. Under the ESPP, an aggregate of 3,000,000 ordinary shares (each ordinary share to be represented by one ADS) are reserved and available for issuance, which were registered with the SEC on August 2, 2017, for sale to eligible employees. Subject to certain exclusions, any employee of the Company’s U.S. subsidiary, Amarin Pharma, Inc., who works at least 20 hours per week and has been employed for at least six months as of the first day of the applicable offering period is eligible to participate in the ESPP. Eligible employees may authorize payroll deductions of up to 15 percent of their base pay to be withheld to purchase ordinary shares, subject to terms and limitations of the plan, at a price equal to 85 percent of the lower of the fair market values of the Company’s ordinary shares as of the beginning or the end of six-month offering periods.

For the offering periods ended on the last business day on or before each of May 31, 2019 and November 30, 2019, the Company issued 47,358 shares and 75,673 shares, respectively, at a purchase price of $15.02 per share and $14.92 per share, respectively. For the offering periods ended on the last business day on or before each of May 31, 2018 and November 30, 2018, the Company issued 127,872 shares and 184,385 shares, respectively, at a purchase price of $2.81 per share and $2.86 per share, respectively. No shares were issued under the ESPP during the year ended December 31, 2017 as the initial enrollment and offering periods commenced in 2018. As of December 31, 2019, 2,564,712 shares were reserved for future issuance under the ESPP.