§ 2705.Disclosure of Facts Or Data Underlying Expert Opinion

Chapter 40: Oklahoma Evidence Code · Last amended November 1, 2002 · Last verified August 3, 2026

In one sentenceLets an expert state an opinion and the reasons for it without first disclosing the underlying facts or data unless the court requires otherwise, though the expert can still be required to disclose those facts or data on cross-examination.

Full Text of § 2705

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An expert may testify in terms of opinion or inference and give reasons therefor without previous disclosure of the underlying facts or data, unless the court requires otherwise. The expert may in any event be required to disclose the underlying facts or data on cross-examination.

Amendment History

Laws 1978, SB 276, c. 285, § 705, eff. 10/1/1978; Amended by Laws 2002, HB 1939, c. 468, §56, eff. 11/1/2002.

Plain-English Summary

An expert doesn't have to walk through every underlying fact or piece of data before giving an opinion -- the expert can testify to the opinion or inference and the reasons for it directly, unless the court requires the foundation to come first.

The other side isn't shut out. Whatever the direct-examination sequence, the expert can be required to disclose the underlying facts or data once cross-examination begins.

Frequently Asked Questions

Does an expert have to explain the basis for an opinion before giving it?

Not unless the court requires otherwise -- the default lets the expert give the opinion and reasons first.

Can opposing counsel force the expert to reveal the underlying data?

Yes, on cross-examination the expert may be required to disclose the underlying facts or data.

Can a judge require the foundation to come before the opinion?

Yes, the statute lets the court require disclosure of the underlying facts or data before the opinion is given.

Source & verification. Section text is reproduced verbatim from Title 12 of the Oklahoma Statutes, enacted by the Oklahoma Legislature. Last verified August 3, 2026. · Official source

Also known as: expert disclosure underlying facts oklahoma12 O.S. § 2705FRE 705 oklahoma equivalentcross-examining expert about basis for opinion oklahoma