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 New Mexico, 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 decisions regarding evidence that was not allowed to be part of the trial record. This is particularly important when no offer of proof was made at trial. The bill of exception details the nature of the evidence and the grounds for its admissibility, providing a basis for appellate courts to review the trial court's decision to exclude the evidence. Both procedures are essential for ensuring that a party's right to appeal is preserved with respect to evidentiary rulings made during the trial.