Despite the Greek notions of supreme power of the gods and fate, Oedipus' downfall is primarily the result of King Laius' and his own actions and attempts to defy the gods, consequently Sophocles says that prophecies from the gods of someone's fate should not be ignored....
This being said, I will argue that this play is actually a tragedy of fate: "its tragic effect depends on the conflict between the all-powerful will of the gods and the vain efforts of human beings threatened with disaster." In tracing the events throughout Sophocles' play it becomes evident that the will of the gods wins out, causing the collapse of Oedipus, his land and the people of Thebes....
(Greek: Oedipus Tyrannus; Latin: Oedipus Rex; Oedipus the King)
"Oedipus the King" is a monument to Sophocles's dramaticgenius, and to the freedom of Athenianthought.Sophocles himself served as an army general.
Oedipus Rex or Oedipus the King Summary | GradeSaver
When Oedipus defeated the Sphinx by solving the riddle, he could have refused to take the missing king's throne. He could have also declined to marry the former king's wife, unaware that the queen was his own mother. He accepted both of these without any regrets. If his decision was different it might have altered the course of events in the future. His personality made sure that the decisions went the way they did. These choices were made by Oedipus with his own free will, his own decisions. He didn't have to accept these gifts, but did none the less. These conclusions would lead to his own demise, but they were his own mistakes, not fate.
Enjoying "Oedipus the King" by Sophocles
Free will can also be found in the actions of Jocasta and Laius. The choices they made were not made by their own judgement, but rather reactions to a situation that neither of them was prepared to deal with. Upon hearing the prophecy that foretold the future sins in their household; they made a harsh decision out of fear. They had little Oedipus sent to die at the foothills of a mountain. This reaction seems very cruel, but back in ancient times it was very natural. Being that an oracle foretold the prophecy, Jocasta and Laius responded as any Greek parents would. They solved the problem by removing Oedipus from the equation, but in the end their decision wasn't the right one.
Oedipus Rex or Oedipus the King Characters | GradeSaver
Yea, Oedipus, my sovereign lord and king,
Thou seest how both extremes of age besiege
Thy palace altars—fledglings hardly winged,
and greybeards bowed with years; priests, as am I
of Zeus, and these the flower of our youth.
Meanwhile, the common folk, with wreathed boughs
Crowd our two market-places, or before
Both shrines of Pallas congregate, or where
Ismenus gives his oracles by fire.
For, as thou seest thyself, our ship of State,
Sore buffeted, can no more lift her head,
Foundered beneath a weltering surge of blood.
A blight is on our harvest in the ear,
A blight upon the grazing flocks and herds,
A blight on wives in travail; and withal
Armed with his blazing torch the God of Plague
Hath swooped upon our city emptying
The house of Cadmus, and the murky realm
Of Pluto is full fed with groans and tears.
Therefore, O King, here at thy hearth we sit,
I and these children; not as deeming thee
A new divinity, but the first of men;
First in the common accidents of life,
And first in visitations of the Gods.
Art thou not he who coming to the town
of Cadmus freed us from the tax we paid
To the fell songstress? Nor hadst thou received
Prompting from us or been by others schooled;
No, by a god inspired (so all men deem,
And testify) didst thou renew our life.
And now, O Oedipus, our peerless king,
All we thy votaries beseech thee, find
Some succor, whether by a voice from heaven
Whispered, or haply known by human wit.
Tried counselors, methinks, are aptest found 
To furnish for the future pregnant rede.
Upraise, O chief of men, upraise our State!
Look to thy laurels! for thy zeal of yore
Our country's savior thou art justly hailed:
O never may we thus record thy reign:—
"He raised us up only to cast us down."
Uplift us, build our city on a rock.
Thy happy star ascendant brought us luck,
O let it not decline! If thou wouldst rule
This land, as now thou reignest, better sure
To rule a peopled than a desert realm.
Nor battlements nor galleys aught avail,
If men to man and guards to guard them tail.