"In blackest day, in brightest night,
Like the Green Lantern Corps, it is not required to say the oath but all members do. When anyone other then Sinestro says the oath, "My power" is changed to "His power".
Sinestro Corps Powers:
Like the Green Lantern Corps, the Sinestro Corps also have rings. These rings allow them to create objects, shields, and many other things (including flying through space). Unlike the Green Lanterns, the Sinestro Corps' rings are powered by their ability to inflict fear on their enemies (them more their enemy fears them, the more powerful they are). Their rings require power. This power comes from the Lanterns that they have. They insert the ring (while wearing the ring) into the lantern and recite the Sinestro Corps Oath.
After the ring's user is killed, the ring will search the universe to find someone with the ability to inflict fear to replace its former user.