How does the author of Oedipus Rex use dramatic irony to create tension?

In Sophocles's Oedipus Rex, the title
character is a classic example of Aristotle's tragic hero.  Oedipus, who unknowingly
kills his biological father and marries his biological mother, is widely recognized as
one of the most unfortunate victims of fate in all of
literature. 

The play opens with Oedipus making a vow to
find the killer of Laius in order to free the city of Thebes from punishment by the
gods.  A genuinely good man who cares deeply about his people, Oedipus vows to stop at
nothing to find and punish Laius's murdered.  The entire speech, along with many other
lines/situations from the rest of the play, can be labeled as dramatic irony since the
audience knows something (that Oedipus is Laius's biological son and murderer)
that Oedipus doesn't know:

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Now, since I am ruler and hold this kingdom

that he held before—holding also the bed
and wife we have both
sown; and children
of the same mother would have been born to us,

had his line not been ill-fated—since chance(270)
has driven me
into that one’s powers,
therefore I shall fight for him in this matter,

as if for my own father, and I shall try
everything, seeking to
find the one who
committed the murder, for Labdacus’ son,(275)
son
of Polydorus, and before him
Cadmus and Agenor, kings of
old.

As the plot of the play
unfolds Oedipus finally comes to understand who he is and what he has done.  And keeping
his word, he banishes himself from Thebes for his actions.