Operating costs can be fixed or variable, and are based on an effective date.
Operating costs can be added from the Network tab by selecting the Opcost URL link, Data Menu - Opcosts, or via the Data tab:

From the Data tab:

Selecting Opcost from either of these menu items will produce the dialog below.
From the effective date and onwards, each month WellSpring will calculate operating costs for the well or facility. These operating costs will continue to be assigned to the asset until either the asset ends or new operating costs with a later effective date occurs.

Operating costs can be assigned at any asset (well or facility).
fn - Will pop up the function editor to specify operating costs as a function of WellSpring variables (See User Defined Functions )
See also