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 Wyoming, an offer of proof is a procedural tool used during a trial to create a record of evidence that the court has deemed inadmissible. This is done outside the presence of the jury, typically after an objection to the evidence has been sustained by the judge. The purpose of an offer of proof is to preserve the excluded evidence for appellate review, by demonstrating what the evidence would have shown and why it is relevant and material to the case. On the other hand, a bill of exception, or formal bill of exception, is a method used to document objections to the court's rulings on evidence that was not included in the trial record because no offer of proof was made. This allows the appellate court to review the decision of the trial court regarding the exclusion of evidence. Both procedures are important for ensuring that a party's right to appeal is preserved, particularly with respect to evidentiary rulings made during the trial.