Exhibit 23

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We hereby consent to the incorporation by reference in the Registration Statement on Form S-8 (File Nos. 333-98435-99, 333-120312, and 333-119309) of NewMarket Corporation of our report dated March 14, 2005 relating to the financial statements, management’s assessment of the effectiveness of internal control over financial reporting and the effectiveness of internal control over financial reporting, which appears in the Annual Report to Shareholders, which is incorporated in this Form 10-K.

/s/ PricewaterhouseCoopers LLP

Richmond, Virginia

March 14, 2005