Expert witnesses play a more critical role than ever in the outcome of product liability litigation. Indeed, in many jurisdictions a sustainable opinion from a qualified expert witness is required to establish plaintiffs prima, facie case. Therefore, it is increasingly important to explore issues that may challenge the credibility of an opposing party's expert witnesses. An important factor in assessing credibility is bias, and a source of bias that lawyers should carefully investigate is an opponent's expert witness fee arrangement. Some forms of expert compensation, such as contingency fees, inherently reveal a conflict-of-interest or an appearance of bias. For that reason, consider not only what an opponent's expert witness is paid, but also how the expert is paid. Uncovering an expert's financial stake in the outcome of litigation to expose bias can seriously undermine the witness's credibility. The obvious credibility issues arising from a witness's financial stake in the outcome of litigation warrants a close examination of your opponent's expert witness fee arrangements.