This excerpt taken from the PKOH DEF 14A filed Apr 18, 2007.
Termination of Employment and Change of Control Arrangements
All of our executive officers are employees-at-will and, as such, do not have employment agreements with us. Therefore, we are not obligated to provide any post-employment compensation or benefits. However, upon a change of control, as defined in the 1998 Plan, all unvested stock option grants become fully exercisable and all outstanding restricted share grants fully vest.