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 Oregon, an offer of proof is a procedural mechanism used during a trial when the court excludes evidence. It allows the attorney to create a record of what the evidence would have shown, had it been admitted. 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 issue for appeal, by demonstrating how the exclusion of the evidence could have affected the outcome of the case. On the other hand, a bill of exception, also known as a formal bill of exception, is a less commonly used procedure in modern practice, largely replaced by the offer of proof. It serves a similar purpose in that it allows a party to detail on appeal the evidence that was not allowed into the trial record. The bill of exception is a written statement by the judge or a stipulation by the parties as to what the excluded evidence would have been, ensuring that the appellate court can review the decision to exclude the evidence. Both procedures are important for preserving a party's right to appeal decisions on evidentiary matters.