An offer of proof—also known as an informal bill of exception—is a procedure available during trial for the presentation of evidence the trial court has excluded. An offer of proof is made outside of the jury’s presence and often after the judge has sustained an objection to the admissibility of the evidence.

A bill of exception—also known as a formal bill of exception—is a procedure that allows a party to complain on appeal about evidence that would not otherwise appear in the trial record (because there was no offer of proof made at trial) by detailing the evidence (testimony, etc.) that would have been offered if the trial court had allowed it.

In Louisiana, an offer of proof, or an informal bill of exception, is a procedural tool used during a trial to create a record of evidence that the trial court has excluded. This is done outside the jury's presence, typically after an objection to the evidence has been sustained by the judge. The purpose of an offer of proof is to ensure that the appellate court is aware of the evidence that was not considered by the jury, which may be relevant for appeals on the grounds of evidentiary rulings. On the other hand, a formal bill of exception, or a bill of exception, is used to document and preserve for appeal any evidence or testimony that was not allowed by the trial court and for which no offer of proof was made during the trial. This procedure ensures that the appellate court can review the excluded evidence even though it does not appear in the trial record. Both procedures are important for preserving issues for appeal regarding the admissibility of evidence.