In the U.S. legal system, winning a case doesn't guarantee that your expert witness fees will be paid by your opponent. That's the "American rule" we're all familiar with--generally, each side pays its own costs of litigation. As explained in a recent California case, expert fees, just like attorney's fees, are not ordinary litigation costs that are routinely shifted as an exception to the American Rule. Like attorney's fees, expert fees are treated differently than ordinary litigation costs because they can be expensive and unpredictable, and could chill plaintiffs from bringing meritorious actions. Baker v. Mulholland Security and Patrol, Inc., B232172 (Cal. App. Mar. 28, 2012). Nevertheless, the American rule is subject to many exceptions, and prevailing parties often have ways to recover their expert witness fees.
Look to Statute or Contract
The U.S. Supreme Court has held that expert witness fees are taxable as costs of federal litigation under Federal Rule of Civil Procedure 54 and 28 U.S.C. section 1920, but only to the extent allowed by statute or other rule. Crawford Fitting Co. v. J. T. Gibbons, Inc., 482 U.S. 437 (1987). Without a statutory basis, your request for expert witness fees is a nonstarter in the states as well, unless the parties contracted for their recovery. The statute can be one of general civil procedure, expressly giving the court discretion to tax expert witness fees as costs in any case. In states lacking such a broad grant of authority, you'll have to determine whether the specific statute sued under allows recovery of expert witness fees. Unless you're appearing before the reincarnation of Justices Brennan and Marshall, you'll likely be unsuccessful arguing that expert witness fees are "costs" within the court's general authority to tax.
By the way, don't confuse attorney's fees and expert witness fees when it comes to "costs." They are separate elements of litigation costs, and statutory authorization for an award of attorney's fees does not mean you can get an award of expert fees. West Virginia University Hospitals, Inc. v. Casey, 499 U.S. 83 (1991).
Fees as of Right, or Are There Limiting Principles?
Many statutes providing for the recovery of expert witness fees give the court discretion whether to allow an award at all. For example, consider the California statute at issue in Baker v. Mulholland mentioned above. California's Fair Employment and Housing Act (FEHA) permits recovery of expert witness fees within a court's discretion. The question before the court was whether to impose some limit on judicial discretion when the prevailing party in a FEHA case is the defendant. Should an award of expert witness fees only be made when the plaintiff's case is deemed frivolous? That's the rule in federal court for Title VII cases, and the Baker court adopted it for California FEHA cases.
Under most statutes and court rules, the amount of an expert witness fee award is left to the sound discretion of the trial court. Courts of appeal won't often disturb the award, recognizing that the trial courts are in the best position to determine the reasonableness and necessity of the costs and reimbursements sought by the prevailing party.
If you're concerned about not getting reimbursed for large expert witness fees, the offer-of-settlement gambit could help, particularly if you are the defendant. In California, for example, except in eminent domain actions, the court or arbitrator may require an unsuccessful plaintiff to pay a reasonable sum to cover costs of the services of expert witnesses incurred and reasonably necessary in preparation for, or during, trial or arbitration.
Before seeking reimbursement for the costs associated with hiring expert witnesses, check all contracts between the parties for fee shifting provisions. Absent any such agreement, be sure you understand your jurisdiction's rules and statutes of civil procedure applicable to cost recovery generally. If the cause of action is statutory, determine whether it allows for recovery of expert witness fees. Finally, be prepared to convince the court that a full award is deserved.