Level Information: This is the first level Super Saiyan-jin or SSJ for short. When a saiyan becomes SSJ his eyes turn green, hair slightly lifts up and turns blonde also muscles slightly expands.
Saiyans that are able to do this level: Goku, Gotenks, Vegitto, Gogeta, Gohan, Trunks, Goten, Vegeta, Brolly, and Future Trunks.

Level Information: This is a level between SSJ and SSJ2 and only shows a short period of time in DBZ. The changes are that a saiyan's hair lifts a little bit higher and muscles greatly! increases, so a saiyan's power has increased greatly but the bad thing about USSJ, is that a saiyan's speed is greatly decreased because of the huge muscles. Vegeta was the first one to do this but realizes that speed is decreased, so he doesn't train much with it but it is his favorite level which at this time he calls himself "Super Vegeta" :). Trunks though hasn't realize about the speed decrease, so he over trained that level and now can become USSJ2 but has so much power that he is too slow to even use it on Cell.
Saiyans that are able to do this level (USSJ): Goku, Future Trunks, Vegeta, Vegitto and Brolly.
Saiyans that are able to do this level (USSJ2): Goku, Future Trunks and Brolly

Level Information: This is a ascended SSJ or SSJ2, the changes are muscles slightly increase, hair lifts even higher, hair is a little bit brighter and there is lightning surrounding the saiyan.
Saiyans that are able to do this: Gohan, Goku, Vegeta and Vegitto.

Level Information: This is the 3rd level of SSJ, the changes are hair is greatly increased all the way to the knee, eye brows burned off, still have lightning surrounded saiyan's body and power greatly increased. This technique was very hard to do for Goku since he hasn't had that much practice with it but later he can transform faster, with all the fighting from buu.
Saiyans that are able to do this: Only Goku and Gotenks.

Level Information: This level is what any Saiyan can do automatic if they had their tail. When there is a full moon they transform into a big monkey beast that increases their power to 10x and the only way to stop it, is to cut off the tail or destroy the moon. Golden Oozaru is just like the SSJ level of a Oozaru, this only shows in DBGT though.
Saiyans that are able to do this: Any saiyan with a tail can basicily do this level.

Level Information: This is the last level in SSJ and only appears in DBGT. Goku was the first one to do this level by having his tail pulled out, so he can get his true power. He turned into Golden Oozaru and was berserk destroying everything but the love of his granddaugher Pan, gave him the strength to take control oozaru and transformed into SSJ4. The changes are very different the changes are hair is back to black, body covered with red hair, red around eyes, tail grown back and personality changes a little. Vegeta was also able to turn into ssj4 but he kinda cheated on doing this (he used a machine that made him turn into ssj4...cheater! lol).
Saiyans that are able to do this: Only Goku, Vegeta, and Gogeta (Fusion of Goku and Vegeta with the fusion dance).