In The Outsiders, when and how did Ponyboy's parents die ?

The Outsiders by S.E. Hinton traces the difficulties faced by Ponyboy and his brothers after the tragic death of their parents which the reader learns makes life very challenging, especially as the eldest brother, Darry is only twenty years old himself. The story begins when Ponyboy comes out of a movie theater and talks about his brothers. The reader is alerted to the fact that Pony's brothers dominate his thoughts. In chapter 1, Ponyboy says that he loves his brother Soda "more than I've ever loved anyone, even Mom and Dad." He also mentions that Darry is strict and has "gone through a lot in his twenty years, grown up too fast."  

Ponyboy and his brothers are members of The Greasers, a gang from "the East Side" and Ponyboy begins to wish he had not gone to the movies alone as a rival gang, The Socs, "the West-side rich kids," threaten to "jump" him as he is walking home. Ponyboy, as the narrator, discusses with the reader how the Socs have no boundaries and "wreck houses" and do other destructive things just for the sake of it whereas the Greasers "have a gang fight once in a while...and wear our hair long" but are more like "hoods." Ponyboy is quick to tell the reader that he and Sodapop try to stay out of trouble or at least don't get caught because he is aware that "since Mom and Dad were killed in an auto wreck" the boys can only stay together if they "behave."

Ponyboy mentions his parents occasionally and in chapter 4 he talks about how he used to go to church, "even after Mom and Dad were gone;" that is until Sodapop and some other Greasers cause a disturbance, and since then, Ponyboy has never been back. After the fire in the church, Ponyboy is shocked that he sees Darry crying and Pony remarks that Darry hadn't cried for years, "not even when Mom and dad were killed" (chapter 6).  

Pony fondly remembers his mother in chapter 8 when he and Two-Bit are talking about Johnny's neglectful mother. Ponyboy's mom was "beautiful and golden... wise and firm..." and Ponyboy admits that Darry is very hard with him, even more so than Pony's own parents but, as Ponyboy points out, Darry has had no practice bringing up a child whereas his parents "raised two boys before me."

All of these references suggest that the parents have probably been dead for about two to three years.