Compensatory (Comp) Time:

There are two types of Compensatory (Comp) time:

Federal
Applies only to non-exempt employees who actually work more than 40 hours in a workweek and who are not paid for those overtime hours.

Federal comp time is computed at a rate of 1.5 times for each overtime hour worked.

Example: Joe Employee works 2 hours of overtime that falls under the FLSA rules. He is entitled to 3 hours of comp time. There are no statute of limitations and this overtime compensatory time will remain on the books until the employee uses these hours or is paid for them.

State
Applies to non-exempt employees whose total number of hours actually worked plus any paid leave or paid holiday, exceed 40 hours in one workweek. In certain circumstances, exempt employees, who worked on a Holiday or Skeleton Crew day, are eligible for State comp time

State comp time is computed on a 1 for 1 basis.

Example: Janet Employee works 2 hours of overtime, that falls under the State comp time rules. She is entitled to 2 hours of comp time.
This State comp time must be used within one year from the date it is earned.

Combination
While the rules are mutually exclusive, it is possible for a non-exempt employee to earn both types (Federal and State) during the same workweek.

More detailed information regarding comp time is contained in UTSA University Policy - Handbook of Operating Procedures:

http://www.utsa.edu/hop/chapter4/4-27.cfm