If you're referring to kitchen's drill (i presume u are).. i believe that thats kinda half-bug/half-feature. When a building is created it copies some of the properties defined in the building.dat.. in particular the number of employees required. At the time kitchen's drill was built (it's actually one of the few original government buildings still left), the oil drill building in the building.dat required less employees than it does now, and hence is more efficient even though it has no employees.
This is a bug really, as all buildings should update whenever the building.dat changes.. somethin i'll fix sometime soon. For now tho, kitchen gets that bonus coz its a special "historical" building
