anchor: We all have learned recently, for example, that even outright lying under oath in a deposition for a civil case is the kind of thing that an ordinary citizen apparently does not often get prosecuted for (though it's not clear why not--especially when the liar is the defendant in the case).
positive: Lying under oath rarely gets prosecuted in the civil courts and there doesn't seem to be a reason why.
negative: It is okay to lie under oath in court.