Stuck Water Shutoff Valve?

[Mac L.]

Need advice on super stuck water shutoff valves in a much older house.  Multiple stuck valves throughout the house and at the main shutoff within the house. We were able to shut it off from outside the house near the street for some quick repairs, but this isn't the best situation. 

Didn't want to force it for fear of breaking the valves. Is there something/a substance we can apply to help loosen the valves?

Any thoughts or suggestions would be greatly appreciated.

Thanks!