(3) Stock-Based Compensation

TripCo Incentive Plans

TripCo has granted to certain of its directors and employees options to purchase shares of TripCo common stock (“Awards”). TripCo measures the cost of employee services received in exchange for an equity classified Award based on the grant-date fair value (“GDFV”) of the Award, and recognizes that cost over the period during which the employee is required to provide service (usually the vesting period of the Award).

TripCo has calculated the GDFV for all of its equity classified Awards and any subsequent remeasurement of its liability classified Awards using the Black-Scholes-Merton model. TripCo estimates the expected term of the Awards based on historical exercise and forfeiture data. The volatility used in the calculation for Awards is based on the historical volatility of TripCo common stock and the implied volatility of publicly traded TripCo options. TripCo uses a zero dividend rate and the risk-free rate for Treasury Bonds with a term similar to that of the subject options.

Included in the accompanying condensed consolidated statements of operations are the following amounts of stock‑based compensation, the majority of which relates to TripAdvisor as discussed below:

Stock-based compensation expense related to TripAdvisor was $29 million and $26 million for the three months ended September 30, 2018 and 2017, respectively, and $90 million and $72 million for the nine months ended September 30, 2018 and 2017, respectively.

TripCo - Outstanding Awards

The following table presents the number and weighted average exercise price (“WAEP”) of the Awards to purchase TripCo common stock granted to certain officers, employees and directors of the Company, as well as the weighted average remaining contractual life and aggregate intrinsic value of the Awards.

There were no options to purchase shares of Series A common stock granted during the nine months ended September 30, 2018. There was no activity during the period related to the outstanding TripCo Series B common stock options.

As of September 30, 2018, the total unrecognized compensation cost related to unvested Awards was approximately $6 million. Such amount will be recognized in the Company's consolidated statements of operations over a weighted average period of approximately 1.8 years.

As of September 30, 2018, TripCo reserved 2.3 million shares of Series A and Series B common stock for issuance under exercise privileges of outstanding stock Awards.

TripAdvisor Equity Grant Awards

The following table presents the number and WAEP of the Awards to purchase TripAdvisor common stock granted to certain officers, employees and directors of TripAdvisor.

The weighted average GDFV of options granted was $17.72 for the nine months ended September 30, 2018.  

As of September 30, 2018, the total unrecognized compensation cost related to unvested TripAdvisor stock options was approximately $39 million and will be recognized over a weighted average period of approximately 3.0 years. The total intrinsic value of stock options exercised was $7 million and $8 million for the nine months ended September 30, 2018 and 2017, respectively.

Additionally, during the nine months ended September 30, 2018, TripAdvisor granted 3,334 thousand of primarily service-based restricted stock units (“RSUs”) and market-based restricted stock units (“MSUs”) under the 2018 Stock and Annual Incentive Plan and the Amended and Restated 2011 Stock and Annual Incentive Plan. The RSUs’ fair value was measured based on the quoted price of TripAdvisor common stock at the date of grant. As the MSUs provide for vesting based upon TripAdvisor’s total shareholder return, or “TSR,” performance, the potential outcomes of future stock prices and TSR of TripAdvisor and the Nasdaq Composite Total Return Index, was used to calculate the GDFV of these awards. The weighted average GDFV for RSUs and MSUs granted during the nine months ended September 30, 2018 was $42.56 per share. As of September 30, 2018, the total unrecognized compensation cost related to TripAdvisor RSUs and MSUs was approximately $253 million and will be recognized over a weighted average period of approximately 2.8 years.