It was his choice to leave his adopted family to escape the prophesy that he knows about. The adopted family however choose even at this point not to inform Oedipus of the true nature of his fate. Another choice that Oedipus makes is to kill Laius at the crossroads, regardless of the fact that the prophesy is very specific regarding where the murder will take place. When he marries the wife of the dead king, it also does not occur to him that this is remarkably parallel to the prophesy. One might therefore argue that Oedipus might have been deliberately blind to the truth of his actions in order to further his own good fortune. On the other hand, Sophocles' aim might have been more towards the literary element of irony that Oedipus' actions create, and towards the theme of the inescapability of fate.

As the play progresses, Oedipus makes choices according to what he believes is the correct thing to do. He shows his integrity of character in these choices. Regardless of the potential danger to himself and his high position, Oedipus nevertheless insists upon finding the truth. This choice leads to the fate that is eventually fulfilled.

It is therefore clear that the ultimate fulfillment of the prophecy is due to the coordination of both fate and free will. It appears that Sophocles' message relates to the fact that fate is inevitable. Oedipus, his birth parents and his adoptive parents could have chosen any actions short of actually killing Oedipus and making sure that he was dead, and the prophesy would have found fulfillment.

If the inevitability of fate is taken into account, one might argue that Oedipus could not have done anything to deserve his fate. He was a victim of a prophesy made before he was born and was therefore destined to tragedy before he could have done anything to deserve it.

Oedipus' Guilt

Regardless of the above argument,...

He acknowledges that his actions were unacceptable and that he could therefore no longer be king. He therefore takes a punishment that he feels is deserving of his actions and willingly surrenders the kingship and his children to Creon. Oedipus' integrity of character also plays a part in his self-imposed punishment. He vowed to find the king's killer and deal with him in kind. When he is revealed as the killer, he believes there is no choice accept dealing with himself as he would with any other killer. For Oedipus, there is no question of guilt, even though he did not know of his guilt or the nature of his actions when he committed the crimes. There is for him therefore no question of his guilt in the matter.
The audience, and particularly modern audiences however, may feel differently about the matter of guilt. The main argument would be that Oedipus did not seek to fulfill the prophesy and kill his own father. Instead, he was trying to escape this. This exonerates him from liability. Nevertheless, the issue of deliberate blindness also has to be considered. Oedipus can be assumed to be well aware of the elements of the prophesy pertaining to killing his father at the crossroads. Surely when he killed the king at the crossroads this should have been a warning sign for Oedipus. At this point he could have chosen not to marry the king's wife. The impression is that Oedipus chooses to ignore these warning signs in favor of prosperity.

I believe that Oedipus' punishment for himself was too extreme, although poetic in its symbolism. While perhaps fitting for the tradition of the Greek tragedy, in today's terms Oedipus cannot be regarded as guilty. He is no more than the victim of forces outside of his control. Although he makes some foolish choices, these cannot be ascribed to willfulness; Oedipus' integrity throughout the play mitigates his guilt.

Sources

Sophocles. Oedipus Tyrannus. http://www.mala.bc.ca/~johnstoi/sophocles/oedipustheking.htm