In Oedipus Rex, to what extent does Sophocles position the chorus in order to create dramatic tension?

Oedipus decides to search for the killer of Laius, both because the oracle has stated that it is the only way to rid Thebes of all its problems as well as because "in righting [Laius] [Oedipus] serves [him]self."  He figures that whoever slew Laius might return to slay him too.  Immediately after this, the Chorus prays to the gods and laments the sad times in Thebes.  When they are finished, Oedipus steps in, rather pridefully, and assures them that he has the situation well in hand.  His pride while addressing them, and his assurance that he can handle the situation (rather than praying to the gods as a more humble man might do), certainly increases the dramatic tension in the play.  Sophocles's audience would already have known Oedipus's story, and so his proud response to the Chorus builds dramatic irony -- when the audience knows more than the character -- increasing tension as well. 

After Teiresias has essentially told Oedipus that he is the killer, the Chorus again speaks.  They are "Sore perplexed" by what the prophet has said, doubting not that he could be wrong because they know he receives his knowledge from the gods.  Again, however, Oedipus stands in contrast to them, doubting everything Tieresias has said and even accusing him of plotting with Creon to take his throne.  To doubt Teiresias is to proudly doubt the gods, especially Apollo, who grants the gift of prophecy.  It is a proud and dangerous thing to doubt the gods and their prophets like this.  Once again, the difference between the Chorus's piety and humility and Oedipus's hubris is quite stark and creates a good deal of dramatic tension.